In regards to powering your AC off the solar / batteries, it is possible, indeed, you are most of the way there. I have not done it personally but others on here have. With you having 2 100ah Battle Born batteries you are most of the way there. The bigfoot will easily take 400w of solar on the roof, possibly a little more if you got fancy. You need an efficient AC and a soft start capacitor and it can be done. This isn't something super high on my prority list but if I was to be full time, I could seriously see going that route. I've had more than a few times of stopping for lunch and it is so dang hot in the camper. The generator sucks gas and poops out when it gets too hot as well. Being able to run the AC on battery for 30 minutes to 60 minutes on battery is perfect for a quick lunch stop.
In regards to the thick cables in the truck, you can do it but I'm not sure it is really worth it. My DC to DC charger is only 20 amps but that is 10 amps more than my 200w of solar. I would have to measure the thickness of the cable but I know it isn't as heavy as welding cables. Higher amperage DC to DC converters are available but remember that you would have to you make yourself a custom 7 pin connector to the camper and rewire the connector in the camper to benefit from all of that. I don't know how much that is worth the effor though. With my 20 amp DC to DC charger, I am using the current cables without issue. In theory it would take about ~5 to 6 hours of driving to charge the battery up from complete dead on the rare occaision that happened. Most of the time after a day of use I'm more like at 60% so a good 3 hours of driving would top that off well enough. That is assuming solar wasn't even available.
The rot situation raised my eyebrows but I think it's very minimal from what I can tell. One thing you should do though is replace all of the exterior screws with stainless steel. Bigfoot used regular screws up until ~2001. My camper was purchased from someone who lived on the coast and he stored it outside. Unfortently, that meant a lot of cold condensation on those screws which meant that over time, the rusted completely out. The majority of screws I pulled from the various cargo hatch frames had no threads on them. Also note that these screws are threaded into pretty much just the fiberglass and possibly some foam insulation. You can't tighten them down tight without stripping the fiberglass. I'm looking at adding a then strip of aluminum or wood as a backing to get more bite when I redo the hatches.
Last thing... Did you have the insulation sucking to the center of your sliding windows? Apparently it was an issue on these campers. I have it really bad and need to get them repaired. Just haven't had the time or money to get to it.
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