New (to me) Lance 815 truck camper owner. Got a few q's

Yes, keep the tailgate on if you enjoy broken tailgate cables from the camper bouncing up and down on it, and a dented/scratched tailgate from all the rocks and road debris that gets kicked up behind your truck. Not to mention the lovely slots you will have to cut into the saddle bags to make it fit.

It's entirely up to you but most leave the tailgate at home, especially considering there are more downsides to having it on than off.