popular rv/trailer accessories

Like others, I think most of the "store items" would be hit or miss. For most folks, they already own stinky slinkys, hoses, blocks, etc., and won't buy at your facility at a premium price (you'll have to be able to beat Walmart and Amazon prices). Things like additives, RV toilet paper, chlorine, etc., are items that only a small percentage of RVers use and buy regularly, so you likely won't get much profit from that (and your stock could sit for years).

Why not ask your actual customers? You might find they'd rather have a couple vending machines with snacks and sodas rather than a bunch of "RV gear".