X2, I bought one that puts out about 14 amps, really simple, mounted it it to the propane tanks, and wired it directly to the battery. I remove the 30amp fuse so the trailer is disconnected from the battery, I think it cost around $20
I take my camper battery out and hook it to a charger, but I use one of these for a truck I keep stored outside. It’s worked fine for years keeping the truck battery charged. About $20.