The process for each panel is;
Measure and size on the bench. Cut then offer onto the camper.
Mark any tweaks then cut and plane several times until bang on.
Rout the bottom edge to create a pencil mould then apply Cyanoacrylate along finished edges until almost sealed, followed by a coat of epoxy resin to protect all endgrain.
Measure and mark out all batterns and electrics on the panel ready for brad nailing.
Spread half a pint of polyurethane glue to all batons then brad nail the panel home with the air gun.
Spend half an hour scooping off and wiping down with acetone all the foaming glue as it oozes out of the joints.
Then after 24 hours the overhanging edges along the top or edges can be flush routed then half round routed before applying a coat of epoxy, sanding followed by filler, more epoxy and fine filler.
I’m using large gaps between panels as my friend to attempt a flat finish, as the panels ain’t perfect and neither are the batons.
I’m knackered explaining it never mind doing it in 80 degrees.