Here's some info on setting up an enclosed trailer that may be of use.
When I decided I wanted an enclosed trailer, I didn't find much online in the way of setting them up. There was some stuff posted over on http://dirtrider.com forums which gave me a few ideas, but not much. My motivation was that my truck can't carry all 4 dirt bikes (2 adult, 2 kids), plus my garage is full of motorcycles and an enclosed trailer would allow me to store some of the bikes outside my garage, freeing up some space. Plus with an enclosed trailer, you can do some bare bones camping with a step up in comfort from tenting it. I wanted a full blown toy box, but I don't have the towing vehicle to pull it with, so that was out, as I couldn't afford both.
Step 1 - Buying the trailer. I decided on a 6x12 enclosed, ramp door, side door and roof vent. That would be big enough to haul 4 dirt bikes, or 2-3 street/supermoto bikes and also could be towed safely by my SUV. I decided to buy used as I knew I'd be throwing money into it. I watched Craigslist for about 2 months before buying a Pace American 6x12 for $2400. I looked at several new and used, with buying a good condition used being by far the best value. $2400 was a little higher than I wanted to spend, but it was a fair price for So Cal and considering it came with spare tire worth $150, and the cabinets. I had already missed out on two others by low-balling. This trailer was originally purchashed from Home Depot for $3000. My intended uses were hauling and storing bikes first, camping in it a distant second intended use. Bikes would include dirt bikes for desert and mx track use, as well as street/supermoto for track days, etc.
Step 2 - Prep. Trailer was bare bones except for some cabinets a previous owner had installed. This is your typical enclosed trailer... butt ugly but useful. I wanted something with a much more finished look inside.
The cabinets were decent so I decided to keep them. A good gloss enamel outdoor paint was mandatory for durability/cleanup/looks, so I opted for a light grey, 2 coats. I re-trimmed the side door with angle aluminum instead of cheesy brown plastic. I pulled the poorly placed d-rings out of the floor as well.
Step 3 - floor. I decided to put a black/white checkerboard vinyl floor in. I found the flooring material on Ebay for $180 (one sheet, 13'x8'). Vinyl floors require a good underlayment, so I installed an APA rated 3/8" plywood over the existing 3/4" plywood floor. This gives a smooth level surface to glue the flooring down. Cutting everything to fit, including the underlayment in multiple pieces, and the single sheet of vinyl flooring took a couple days. I glued the entire floor down, and used a rented 75lbs roller to finish the job. I can't emphasize enough how important the underlayment is. Vinyl floors show every imperfection of the subfloor/underlayment, so a smooth even surface is mandatory. The vinyl will crack along any seams that aren't even from the subfloor.
Step 4 - Bike hauling. I need to haul 4 dirt bikes (2 adult, 2 kids), or 2-3 street/supermoto bikes. For the full size dirt bikes, I love wheel shoes. These work really good, no tie downs. Just roll your bike into it and fold the arms over top of the front wheel. I put two in for the 2 adult dirt bikes, mounted diagonally. I can then put the two kids bikes in with simple tie downs For the street bikes, I have 2 Pingle removeable wheel chalks - not yet installed. These will be mounted parallel to one another, and when removed, only some very low profile mounts remain on the floor. As for tie down points, I opted for E-tracks on either side and the front. If I need tie down points in the very back, I will install a couple flush mount d-rings. To install the E-track, I put stainless bolts where there was angle iron underneath, and 1" heavy duty wood screws in every other hole. This is probably overkill but I don't want anything coming loose or pulling off the floor.
Step 5 - Ramp door. After slipping on it after a little condensation collected on the latex painted door, I knew it needed a Rhino or Line-x coating. Durable and non-slip, much nicer look as well. Pricey for sure, it cost me $275, but I think its worth it. I wouldn't want to be loading bikes in the cold/wet on that original surface.
Step 6 - Misc. A few hooks for hanging stuff, plus a bunch of small d-ring tabs on the walls will give me ample use of the vertical space. That's really the key to these enclosed trailers, using the vertical space for things like tables, chairs, awnings, etc.
Futures: I'd like to get a Mr Heater portable propane heater for the inside, I'd like to mount the spare tire on the outside of the trailer, but I can also get an attachment arm for the e-track if need be. A mesh covering over the open shelves in front so stuff doesn't fly out. Some air mattresses that fit in this space. I need something to hold my gas jugs, and a few other odds/ends.
When I have the trailer full of bikes and gear I'll post some additional pictures so you can see what it looks like full.
Materials & Cost:
Trailer - $2400
E track - $100 (for tracks and attachment points). I bought mine from Industrial Metal Supply in Kearny Mesa, but you can also order online. I got a couple 10' sections, and 1 5' section. I also bought several of the attachment pieces for tie downs.
Vinyl Floor - $200, purchased from Ebay from seller http://stores.ebay.com/Tiki-Toes
Wheel Shoes - $48 each, from Prohoists, also purchased off Ebay,
Ramp Door Line-x Coating - $275
Removable Wheel Chocks from Pingle, $60 purchased from Cycle Gear
Hardware/fastners - $150, purchased from Marshalls Industrial Hardware. Everything is stainless steel. It adds up.
Paint - $40, Home Depot.
Total: about $3300