Rather unexciting but useful:
Three permanent power sockets plus switches plus control LED plus digital voltmeter plus handy ground socket for multimeter, squeezed together in a tiny case mounted to the side of the cubby box.
Heavy (really) duty cargo net spread under roof. Great for damp or bulky stuff - sleeping bag, insulation mat, towels, wet laundry. (Dealer's picture.)
Favourite: homemade roof clamps. Indispensible for attaching the homemade canvas awning and other stuff. Simple but really sturdy.
BTW: lovely forum!
Norbert