My only concern in this area are things like the molded "end caps" for the trailer. These things seem pretty "specific" and I doubt you're going to find them at your local RV repair depot.
Most of the other parts can be worked up out of existing materials. And, most of the mechanical parts are off the shelf (except possibly the guide rod and maybe the pulleys).
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