Sounds like you are on the right track with the wiper problem. My 'new to me' '88 E150 wipers were broken - the dash switch was damaged. I had to order the part from Rock Auto - great place for older vehicle parts! The wiper switch in my late Dad'...
Interesting project! I too have recently bought a van, a 1988 Ford E150 Conversion Van. Still taking care of some mechanical issues before doing the camping conversion. I will likely use some of your ideas.
Without decent All-terrain tires and more ground clearance, it's not going far off pavement. That long wheelbase will increase the chance of high-centering too. Good first try, but not fully thought out yet.