Is the rubbing only on big bumps or more regularly? Fitting coilovers (Gaz or similar) will stiffen up the ride and raise it marginally, but if you're already running close to the arches, then your only options are to fit lower profile tyres or raise the van up to clear them.
If it's rubbing when going over cats eyes, your tyres must be very close to the arches. I would advise as per my previous comment, new shocks / coilovers isn't going to be enough to cure it - you really need smaller profile tyres or a van raise.