Scott, after the asbestos cleanup, noise/vibration concerns me the most. There is already access to fresh air, gas and an exhaust path. The generator would probably create much less heat that the dual Eberspächers.
There was a company making a roof AC unit that could start on a honda eu2000i reliably even at altitude but when they switched refrigerants consumption went up about 15% and they no longer make this claim. There are lots of tricks. A delay circuit which starts the compressor a few seconds after the fan decreases the surge current a bit but more importantly the fan wakes the generator out of eco mode. There are devices which disengage the start coil on the compressor much more quickly based by electronically detecting motion and are much less wasteful than thermal timers or centrifugal clutches--that and you can get a eu2200i in the same form factor as the eu2000i.
A 13.5k BTU AC will cool 400 square feet. The smallest roof top ac made these days is the Coleman Polar Cub (1320 running Watts) At 9.1k BTU it is still gross overkill for a glorified 47 square foot foam cooler
Mike
New owner of Swiss 1975 712AMB.