Just bought a Fiamma one (from JK) a few weeks ago - works really well. Apparently it can allow leaks where the top 'hook' brackets squeeze the rubber seal, but no big deal. Really easy to clamp the bikes to (no straps etc) and I load 2 biggish full-sus mountain bikes. However, you may need longer arms to fit bigger bikes, as the ones JK provide are pretty small. DO NOT BUY THESE FROM JK - they charge a fortune - get them from the main importer and they are a lot cheaper! I'm going to get another arm or 2 as at the moment I am using one to fit first bike to rack, then the other one to fit second bike to first bike, if that makes sense.
JK claim it is an 'exclusive' developed for them - thats rubbish, you can get the same kit from the importer - see here:
http://www.agentfiamma.co.uk/erol.html#3863X0
To be fair, the JK price for the initial kit is pretty much the same, but the 'extras' are more from JK. I bought mine from JK in person, so avoided postage, and I shall still use all the bits that came with the JK 'kit', its just that I shall also buy a few more parts, if you see what I mean.
As far as damaging the van, I think as long as you use the provided padding and film, it should be fine.
I'll take some pics with bikes on if it is usefull...