I saw a USB powered fan and light at the Dollar Store ($3 & $2) and figured I try them in the van. USB power can be supplied via battery or grid power so it's versatile for use in a van.
USB powered accessories.JPG
The fan might come in handy to move a bit of air around in the back section of the van.
The USB light is a quick and easy fix to solve the problem of inadequate reading light for the swiveled passenger seat. The solar controller is located near there and it has two USB outlets.
USB powered accessory.JPG
I don't know if there is a parasitic draw associated with those two USB ports