The other thing I haven't seen mentioned is that you are converting USED freezers. I read somewhere (in support documentation for my deep-freeze I believe) that these things aren't really made to be warmed-up once they are down to freezing temps. Apparently, a lot of them tend to start rusting inside the walls once they get some moisture in there. Since that nearly always happens when they warm up, you can see the potential problem.
I haven't done any investigation myself, but it's something to consider, at any rate.