This is one issue we run into a lot when installing units. That's why we push the submount tank for slide-in units so much. Plus an electric hose reel allows you to push that vac reel back a little and do a dual-stand bracket in front of the vac reel and save that space on the side. Putting a reel on a door isn't a good solution, in my opinion.
The only real option would be to move the hose reels to the other side of the van, take out the chemical shelf (if there is one) and get a chemical holder that fits on top of a fresh water tank. That way when you put the reel on a stack bracket off the side of the vac reel you still have an isle to put equipment down.
Hope that makes sense. If you want to snap some pictures of the install and send it my way, Chris Pond and I will take a look at it and shoot you some ideas to give you a little more space.