Theoretically you can work the ampacity formula with X/12ths of a foot and get just how many amps a 4" long piece of 10ga. wire can handle. It's impressively high.
Practically I think that unwise unless there are very compelling and unusual circumstances. Run the same gauge wire cable as elsewhere in the circuit.
In the old camper I did the same as Vic, breakers mounted as close to each battery bank (truck and camper banks) as was reasonably possible. Solar connected directly to the battery. I placed the old camper's breaker in the circuit such that if you turned it off and either disconnected the Anderson connector or turned off the truck breaker then the whole camper was electrically dead.
I've yet to do the camper end of the new to us camper. Access to the backside of the outside accessible battery box is severely difficult and I've not yet worked out exactly how I'm going to do what needs to be done for the install to be safe. I did install a Blue Sea Systems 150A battery terminal fuse right at the battery + terminal just in case the less than ideal OEM wiring develops a short. Due to necessary distance from the batteries I'll likely leave that in place once I install the breaker.