I put two batteries (connected in PARALLEL) in my trailer because we primarily camp where there are no hookups. (Boondock camping). Having two gives us more electrical capacity - the power lasts longer between recharging cycles.
If you camp primarily where you would be hooked up to "shore power", then you would not see much benefit from having two batteries. But if you boondock, then you'll appreciate the added capacity.
Hi-Lo 1707T - Tire Minder TPMS on Tow Vehicle and Trailer, 300W Solar Battery Charger, Equal-i-zer WDH
2014 F150 Platinum 4x4 3.5L EcoBoost SCrew