Interested to see how you are able to route the cable internally. I pondered doing the same thing, but possibly switching to a 50A main fuse panel, and replacing the incoming power cable to handle 50A then routing the cable from there somehow.
Not really sure we actually need the second AC, just pondering for now.
To be honest we probably just need better interior air circulation, so a fan might suffice. The temperature wasn't too high even camping here in FL in late July, though the main 15K a/c did take a while to cool the 5er down.
I'm pretty handy, albeit slow, at larger jobs like these, I just have no idea how I'd route the cable
2015 Rockwood Signature UltraLite 8281WS
2016 Ford F-250 Lariat CrewCab, 4x4, 6.2L V8