Your van looks awsome, well done. I use mine for kite surfing (dont shout at me) and trying to plan my layout to carry all my kit so looking forward to seeing your van come along.
Re. Ventilation, I think it would be a good idea to have the kit storage area vented to help it dry out, I know my surfboard bag is still damp after a few days if left in the van so venting would be a good idea, ducting in from your heater and an external vent sounds a good solution to keep the airflow. Could you utilise the rear slam vents? or put a vent in the floor?
I’m no kiter hater - quite enjoy it myself! I’m primarily a windsurfer but will be learning wing foiling this year too.
I’m honestly not sure if the slam vents will be adequate given the amount of moisture. Wondering about mounting one or two wind powered roof vents on the empty space behind the pop top next to the sat nav aerial. While I’m not keen on cutting another hole in the roof it should help keep the van (and kit inside!) cool on sunny days as well as create a good airflow. Have started to look for something low profile. Anyone else fitted these?