I decided to go ahead and get the propane tank and access door, THEN figure out how to cut the hole and mount the tank. Not to mention how to seal up the rocker panel.
Here is the tank. Since it will be accessed from the side through the door, the valves are pointed horizontally instead of angled down like many tanks. It also has a shorter tank protection plate than standard tanks, so I won't have to cut it off. It even has a nice rubber trim piece around the edge of the protection plate.
The access door is very nice and was quite reasonably priced. It is made out of a fairly tough and hard thermosetting resin (plastic) which can be painted to match the van. The frame is curved to match the curve of the van body. The hinge pin and latches appear to be stainless steel. It doesn't have a gasket for the door, but I might add something to prevent any rattles.