Auto store etc have auto chargers that will solve the battery charging issue. Sure they may require some setup every time you charge. But so what because if you're like us the Alaska cross off the bucket list trip turned into an adventure far beyond the bucket list. ??????
20A should be plenty based on your post and possibly less. Get a 3 stage one and enjoy the rest of the trip.
While I'd never dismiss having a trip issue I meet a guy in Dawson Creek that bent his 5er hitch. And it was day 19 of getting the parts for repair. But he was determined to continue the trip. Another dropped a trailer axle. Another with engine issues decided to take the ferry from Haines to Vancouver Island.
So what's a little charging among friends???