Re charge via trailer wires ,I do no probs. Easy to work out battery required.
If you can afford 100ah sealed agm go for it, You'll use it as a remote power source
as in able to move it around camp ,home etc, why get a 50 AH battery, same weight/size
and maybe $30 cheaper. If your second AUX goes in the patrol you have a replacement straight away.
just add up all amps of what you intend using