Me, my dad and some of his/my mates once took a VW camper around the UK, was a really good time so i hope this works out for you im no expert on anything that's been said here but couldn't you add Solar panels on the roof to provide power? if not for the main battery then maybe for interior stuff? and yeah from the looks of it those wind turbine things would provide way too much drag, i think the closest i have come to refitting a van has been watching the super bus project videos Knux has put up on the youtubes (also well done on the book knux! ) but i have done some engine work at the local garage and rewired a few dash's at my mates dad's car dealership, anyway if you get it running i hope to see it around soon, i may be going on some type of road trip soon...maybe the states? or Europe? meh its all good
good luck matey!
Jack