I've used the coolbot and it worked like a champ! When I lived in San Diego I helped a retired butcher/hunting buddy who is now a wild-game only butcher set one up in his walk-in cooler (6'x14') after his "real" compressor failed. Much cheaper than an actual compressor and worked great. It's on it's 3rd year now and still works as good as day one. He has no problem keeping his cooler at 38 degrees and can go cooler anytime he wants to. The key is to have a very well insulated walk-in. It won't get down below 40 degrees if you don't get it well insulated.
That same buddy helped me set mine up in my garage in San Diego. Mine was only 4'x4'x6' and used a smaller a/c unit. I had no trouble keeping it at 38 degrees even in the early season when temps at the house could get well over 100 degrees outside and it was only running about 30-40% of the time. I could run it down to 34 degrees with temps in the 90s (warmest weather I ever tried it in) but never saw the need to run it that cool. As long as you're under 40 degrees you're good for a week to 10 days.
You may want to look into one of the portable coolers. Game Keeper Coolers makes on called "The Cube" which is the cheapest I've found. It can be a royal pain in the ass to get your homemade walk-in sealed correctly. I had the help of the professional and he had some spare parts/pieces laying around or I wouldn't have made my own. It's not much more expensive...you're looking at close to a grand or more to build your own and use the coolbot and an a/c for cooling. I just looked at their prices for The Cube and it's gone up to $2200 and change this year. They're stand-alone and run on a 110 outlet. No reason you can't throw them on a trailer and haul them to deer camp either. Guess it would come down to how much you want to play Bob Villa and build your own or do you want the convenience of plug and play and the ability to have it be portable.
Of course, now that I've moved to Florida, I've gotten lazy and haven't gotten around to building another walk-in so I'm using an old fridge on the back porch. As long as you remember to put in a small fan to circulate air, that's actually tough to beat. I took all the shelves out and ran eye-Bolts through the roof to hang it from...just used a 2x4 across the top to run the eye-bolts through so they wouldn't pull through. It's working for now. I've actually been watching the interweb pretty closely lately watching for a small refrigerated trailer with a broken-down compressor that I can get fairly cheap. I'll rip the compressor off and put my coolbot in it and be all set.
