I suspect that you'll find even 10 ga. wire in the charge circuit to be
slow at charging the battery. Over that distance the voltage drop will be too great for anything more than a trickle charge.
For over 40 years, Ancor has been the market leader in Marine Grade® wire and wire management tools. All of our products are built for the harsh marine environment and conform to industry standards.
www.ancorproducts.com
For a reasonable ampacity I'll suggest looking at Anderson connectors. Like this:
SB120 SB Series 120 Amp Anderson Powerpole Kit The full product range:
DC Power Products | Powerwerx
For a max charge rate of 80A at less than 3% Voltage Drop to our slide-in camper's batteries I used the SB120 connector with 6 ga. cables. Seems like massive overkill, but the total circuit length (have to include the ground path/wire/cable) and less than or equal to 3% Voltage Drop really drove up the conductor size. I chose 3% max to keep the voltage high enough to actually charge the battery. 5% drop wouldn't do it, at least not very fast. At the time there was no solar on the camper, so the truck's ~120A alternator had to be able to bring the camper batteries back up in less than a day's drive.
I like to run a dedicated battery hot clear to near the rear bumper of all of my trail & tow rigs's. I use a 285 Series manual breaker (
Eaton Bussmann 285 Series Resettable Circuit Breakers Surface Mount up to 150A), usually an 80A, at the battery tap, and place isolated studs at likely spots along the run. Makes it easy to get battery power for whatever I add to the rig. I use the manual reset version because it is also a simple on/off switch should I need it.
I used powerwerks pages for simplicity but I don't think that I've ever bought anything from them. None the less, they appear to be a good vendor and have been around for a while.