Even tho you may not plan on camping off the power grid you still may have a need for the trailer battery.
You will need to have enough battery 12VDC power to activate the trailer brakes in case of a trailer disconnect when being towed.
There are a few trailer setups that depends on the installed battery to aide in opening the slides or other high current DC operations you may have installed.
In my case my OFF-ROAD POPUP trailer setup with multiple batteries installed becomes my emergency source of 120VAC and 12VDC power for the house requirements when extended power outages are on-going from bad weather and hurricane periods. It certainly has been a blessing for us having this PLAN B setting in the back yard when these Power emergencies come up...
The battery you chose must also be compatible with the charging characteristics of the on-board converter/charger system as well.
Just a couple of my thoughts...
Roy Ken