I have such a trailer for event photography...
It's a 2009 United (brand) V-nose cargo trailer, called a 7x19 by the manufacturer, but the usable "box" area inside is closer to 7x16, plus some extra for the V-nose. The interior height is about 6'6". The trailer has a conventional RV-style side door, a rear ramp door, and opposing marquee-style concession windows. It has finished floors, walls and ceiling, and was all pre-wired to my specs, with six AC outlets, low-profile flourescent light fixtures, and a roof-mounted RV-style air conditioner. The trailer currently has four viewing stations, a server, and a "printing station" PC - six computers in total. I currently have a Kodak 9810 (8x10) dye-sub printer and a Canon Pro 9000 II printer (very nice inkjet prints up to 13x19) in the trailer. I run everything EXCEPT the roof AC on a single Yamaha EF2800i generator. That one generator is not beefy enough to run all the computers AND the AC; I often tap into land-line power on days when I want to run the AC.
(OH...the trailer happens to be for sale.)
I've had three similar setups now, dating back to 2002. I sold the previous two rigs and kept replacing them as I went, making improvements/tweaks each time. This time I think I may just call it quits - at least with the trailer approach. I'm recently divorced and my daughter is off to college, so my "built-in" help has gone away. I think I'll continue to shoot events, but with a smaller/temporary setup...and I'll lean more on the online sales. (Without the benefit of onsite show-and-sell, I fully expect my sales to drop by 50-80%, per event.)
Mike (MT Stringer) mentioned culling and preparing thousands of images being an issue...and it is. But it's one that I solved...
I shoot a lot of motorsports events. Let's use motocross as an example. On each bike, there is a number plate. I take the photos, shooting each separate sub-event (in this case, "motos" or heats) into its own folder on the compact flash card; then I hand off the cards to my assistant in the trailer. The images are downloaded, and the download program (which I authored using Wise Install Master) automatically adds text in the filenames, which correlate to the folder on the CF card from which the images were pulled. A separate .ini file is used to store information - an identifier - to go along with each folder. For example, in the .ini file, I might specify "80 A+B" for folder 100, "80 C" for folder 101, "250 A1" for folder 102, "250 A2" for folder 103, etc. The resulting image files then have the appropriate information added into the filenames. If there are no sub-events, I simply use a common identifier string for EVERY folder specified in the .ini file - perhaps the venue, organization or event name.
The second step is to sort the photos. Again, the sorting program we use is something I've developed/written myself. Essentially, the program displays each photo in the folder where the "unsorted" photos have been stored (by the download program); the program then displays a pop-up box which prompts the operator (my employee) to key in the bike number, as they should be able to see by looking at the number plate on the bike in the photo. This keyed input becomes part of the destination folder's name. You could do the same for athletes wearing numbered jerseys, for marathon runners, and so on. The sorting program also provides the opportunity for the operator to 'trash' a photo, by simply pressing "t" (for "trash"). Since we're mainly entering numbers, the sorting goes very quickly; you just key the digits on the keyboard's numeric keypad and press "Enter". Behind the scenes, the program determines the "destination folder" name; the name is a combination of the keyed input - let's say, (bike number) "259", plus the (moto) identifier string, which is taken right out of the JPG's filename ("80 A+B", for example). So the destination folder name would be "80 A+B - 259" in this case. The sorting program checks to see if there's already a folder matching that name, creating the folder if it does not already exist, and then it copies the file to the destination folder, confirms it's there, deletes the original from the "unsorted" directory, and then displays the next image and provides the next pop-up dialog box.
The program is lightning-fast; nearly as quickly as you can determine whether the photo is a keeper, then key the competitor's number and press Enter, the program does its thing. I'd estimate it takes just under a second per image for all the background processing.
So now imagine you're a motocross rider at one of the events I've shot. You walk by the trailer sometime after your race, and you walk up to one of the monitors. There is a mouse, but no keyboard. The viewing program (we use ACDSee 5.0) is already open, and you see a list of folders all down the left pane within the program. You're a 125 C rider, and your bike number is 399. You see a folder called "125C - 399", and you click it. Just like that, your photos (and only your photos) are displayed as thumbnails in the right side of the viewing program. You can double-click any of the thumbnails to see the full-screen version, and you can scroll through all the full-screen versions using the wheel on the mouse. You can also decide very quickly whether there are enough photos of you from that event to warrant a CD purchase; you don't have to look through literally thousands of unsorted photos of everyone else, then try to remember how many there were of you, where they are located, etc...
No, the sorting program is not for sale as a standalone product. That sorting program is the primary thing that gives my event photography service an advantage over every other service in my area. No other photographers make it that quick and easy for event participants to find and view their photos. I really can't begin to estimate the real value of that sorting program, but for my business, it has been pretty much priceless.
That said, whomever buys my trailer will get a copy of the program.
One other thought about event photography concession trailers: I've seen them both ways - with viewing stations accessible only from the inside, and other trailers where the viewing stations are accessible from the outside. I STRONGLY prefer keeping the customers on the OUTSIDE of the trailer. First, it automatically increases your physical security. It's hard to steal things you can't reach. It also reduces your liability as a business owner; you don't want someone accidentally banging their head on something inside your trailer, or slipping on your steps or ramp. It also keeps your trailer cleaner; no muddy/dirty event participants tracking all that dirt inside your rig. And finally, it gives you a LOT more room to work with, meaning you don't have to have a huge trailer (and a huge truck to pull it with).
I'm pretty damn happy with the setup I've got, but with my help going away, and after eight years of getting up early and doing events all the time, I'm ready to take it down a notch.
If you're interested in buying this setup as a turnkey deal, PM or email me; we'll set up a phone call. The price is negotiable, depending on exactly what you want to get with it. For example, you may want to provide your own generator, or use your existing inkjet printer. For reference, with everything as it sits, the price is $19,000 (a good bit less than it cost to put together in April of '09).
Some intrepid photographer/entrepeneur will be getting a finely-tuned money-making machine that will easily pay for itself the first year...