This post is about converting a rather standard enclosed cargo trailer into a travel trailer suitable for a full-time RVer. Obviously the cost will be less for a weekend camper.
Usually I don't write or read about so-called practical issues, because practicality depends so much on individual circumstances, which usually don't match well between the reader and the blogger.
I'll make an exception today because it is so hard to find the bottom-line cost of converting a cargo trailer. Why the conspiracy of silence? I could speculate on the reasons, but let's let it pass, and instead try to redress the information gap.
Since the RV industry makes expensive junk, it has become more popular to convert an enclosed cargo trailer into a travel trailer, in order to optimize your camping lifestyle, comfort, and low cost. You then tow it with a moderately-priced pickup truck or van.
|A small window was added to the door and the driver's side, after this picture was taken. But what really counts is being able to camp in places like this.|
There is a discussion forum dedicated to these conversions,
http://tnttt.com/viewforum.php?f=42 . It is quite useful if you can be patient with the usual frustrations of public discussion forums. Be skeptical about the advice in this forum: I'm not sure if most of these guys really go camping with their conversions, or whether they just enjoy woodworking, designing, out-shining the Joneses, etc.
But I noticed something strange. Despite wallowing in microscopic details, they seldom mention the 'bottom line' regarding the weight and cost of the conversion.
My cargo trailer is a standard size for a single traveler: nominally 6 foot X 12 foot, single axle, standard steel frame with an aluminum skin on the walls, with a blunt V in the front. It has proven to be the perfect size.
(Cargo trailers are sized rationally, by the size of the box. Travel trailers are sized by the total length, even out to the hitch. So a 6 X 12 cargo trailer is the same size as a 6 X 16 travel trailer.)
Weight: a naked cargo trailer of my size weighs 1400 pounds with brakes. When the conversion was done, it weighed 3000 pounds, which amazingly enough is the nominal GVWR.
(Even more amazingly, the weights on the left and right tires were equal, to within 10 pounds!)
Well, what do you think? Is adding 1600 pounds  during the conversion good or bad? Note that the 3000 pounds was weighed on a scale, and it contains all my stuff for real living.
Footnote  may convince you that I am not cheating by ignoring something, and that the grand result is self-contained for hook-up free camping.
Although I was surprised how much the little things added up to, in weight, I am happy to be able to downsize my next tow vehicle. Essentially it will be the same as for towing one of the larger fiberglass trailers, like the Casita.
|The inside standing height is 6.5 feet. It takes a bit of looking to find that extra height at a dealer's lot. The standard stripper height is 6.0 feet. That might be OK if you are under 5'9" tall.|
Cost: The trailer was bought off a dealer's lot for $3000. It included an RV side door, a ramp in the back, and 15" tires. But a standard trailer off a lot has those dreadful 4 inch drop axles, and no brakes. Half the reason for doing the conversion is to escape the low ground clearance of lightweight travel trailers. So I swapped out to a straight axle, resulting in excellent ground clearance.
|The cargo trailer has this kind of ground clearance after the straight axle was installed. And the springs are UNDER the axle! I could switch to a bigger diameter tire when the time comes. No drain plumbing dangling below the trailer. Success.|
You can get brakes added after you buy the stripped down trailer from a dealer. You get this done at a trailer shop -- which usually is not an RV dealer.
So, after swapping to the straight axle and adding the brakes, the naked trailer was now up to $4000.
Now we can proceed to the cost of the conversion proper. Be prepared for the total conversion cost to come in a lot higher than the low-ball numbers bandied around on the internet. Most of those guys never really kept track of the cost.
Most do-it-yourself projects start off with naive expectations about saving vast sums of money. The mind gloms onto a couple of the larger expenses and ignores the thousand-and-one small expenses.
The final cost of the converted trailer was $11,500. Therefore the conversion proper cost $7,500.  This is no clerical error. All receipts were saved. No costs were hidden by moving "off budget," which is the usual accounting trick. I double-checked the total from the receipts by looking at the total of the withdrawals from my bank account.
I hope you aren't disappointed with that number. Remember that this was a conversion for a full-time RVer who wants the same level of comfort as in a conventional travel trailer. You could take the opposite approach, treat a naked cargo trailer as a hard-walled tent, and make piecemeal improvements as funds permit.
I would do this again. Remember that it only uses the skills that any home-improvement enthusiast has.
 A 5 gallon jug of drinking water, a 5 gallon porta-potty, food in a 12 volt compressor-based refrigerator, two burner propane stove, small sink, large and pretty laminated kitchen counter-top, clothes, tools, office chair, etc.
It only includes one small (5 gallon) tank of propane, four deep-cycle flooded 6 volt batteries, and 480 watts of solar panels.
The conversion did not add a water heater, awning, or microwave. The spare tire is put inside the tow vehicle. Most of the drinking water is in 5 gallon jugs in the tow vehicle.
 But surely, you say, I must have been extravagant. I could supply character references if you like that less than $50 was spent on making things look pretty.
A) But...but...you could have knocked the four batteries down to two, you say.
Well yea, but then you just cycle the batteries deeper and they don't last as long. How does that save money?
B) But...you could get by with 320 Watts of solar panels instead of splurging on 480 Watts.
Well yea, but by adding that last panel ($200), I was willing to do without a generator. These days, skimping on solar panels is false economy.
C) But...you could get by with an ice chest. Or restrict your diet to brown rice and oatmeal.
Give me a break. Besides I carried over a used ($500) Whynter refrigerator from the old trailer. So the $11,500 total does not include a refrigerator. Is that cheating? I don't think so, because everybody probably has a certain amount of stuff from the basement, garage, or old trailer that they will move into the new trailer for "free". In my case, it was a $500 refrigerator, and that is all.
D) But...you don't really need a water pump to survive. You could use baby wipes, and wipe a little here, and a little there.
Big deal, a water pump costs $80, and is one of the real success stories of RV technology. It gets used 30 times per day, and will last for the next 20 years. It spares you all that spillage. And how do you take a shower, or clean anything for that matter, unless you rinse it off with pressure?
E) But...you added two small windows and a Fantastic fan roof vent. Your trailer would be more stealthy if you had omitted those extravagances.
This is not a stealth cargo trailer. You are at the wrong blog if you are interested in that.
F) But...you shouldn't have wasted all that money on fancy woodworking, exotic paneling, imported Italian granite countertops. (eyes rolling)
Once again, character references will be supplied on request...
G) But...you included two months of rent in an RV park for the conversion. You could have done it at an LTVA or in a national forest and saved a fortune.
Yea right, transportation is free. Do you have any idea of how many trips you take to the hardware store on a project like this? In my case, it was three shopping expeditions per day for 2 months.
I had great luck by finding an RV park in Farmington NM that let me boondock the old and new trailers, side by side, in the storage row in back of a regular RV park. He charged a total of $175 per month. I was a couple miles from Home Depot, Lowes, Walmart, Ace, a trailer store, and even a metals supplier.
So I had it as good as it could be. Still, all that running around was ridiculous. I included $500 in the total for transportation and eating-out during the conversion.