tooldad1041 yes if your truck indeed shuts off the charge line when not running then camper will only draw from camper battery-effectivley truck isolates itself so solenoid not needed. Only benefit would be running a larger charge line directly from source. Could be done later if you decide you want faster charging etc.
So your good to go-just add battery, when truck is running it will charge-when off camper cant drain truck and only use new battery.
As to where-if its not prewired for battery I would assume installing inline as you said on the 12v feed. I would think a positive disconnect on 12v feed to camper if it doesnt have one (sounds like not) to ensure no loads when stored. I assume since no pre wire for battery you only have an inverter and not a charger. So maintenance will only be by truck or other manual means.
pezvela at least on our 01 Ford F250 drivers side frame has the Ebrake cables and some bracketry that complicates use on drivers side. I had the opportunity to install one but didnt-specifically where its supposed to go on passenger side , forward of spring perch rear of T/L camper mount plate, is where my air tank is-plus as you noted a lot more wireing. Everything; charge lines, source, camper batts, wireing is on drivers side.
To utlize on drivers side would require some custom standoffs and cutting/ extending the TL clamp bits to reach, doable if I had a tl bracket to start otherwise just making one easier. I abandoned the whole project due mostly to mian camper battery dumped and some other issues.
