The 835 has seperate black and gret tanks. 8 or 9 gal each I believe.
The 815 has a combined black tank with the shower draining into it.
The 835 is a good camper for a LB but will probably work with a SB.
I don't think the wing boxes will make a difference in aerodynanamics. You are carrying a brick on back of your truck. You will need to arrange to move the brake/taillights to the rear of the camper.
For the same price, I recommend he gets the 845, the same camper made for a SB with more storage and bigger tanks. Also the option for built in generator.
13Jeep Wrangler
07 Ragen 21FB
12 Yamaha Super Tenere
14 Suzuki DR 650