Proeddie, Do you have links to those vents?
We generally recommend vents towards the back
for better flow through and less noise if it's open
while driving.
What about something like this in the rear door:
http://www.ebay.com/itm/112432117146
I ordered one so will let you know how it looks/works.
We have a horseshoe vent in the rear door of our Sprinter
with a bilge van for pulling stinky smells out of our bathroom
Link below. Our bilge fan is not quiet but others might be.
All the best,
Hein
DIYvan.com
[ame]https://www.amazon.com/gp/product/B008OJ7J62[/ame]