If anyone is interested, I have a roof-rack for sale for a Mercedes Sprinter Long Wheel Base van. Bought the van yesterday for the business, but the roof rack is surplus to requirements! They seem to be £600 new, so we thought we'd list it for sale. Might help pay for the extravogant "worm" livery I'm going to get put on the van! Any interested parties PM an offer ;-)
Why not make a huge fibreglass worm and stick it on top of the van, sure to get you noticed. Where I used to live, someone had a big plywood cow on the roof rack of there car, they parked the car outside of the local training estate to advertise their tool sales company where local planning regulations would not allow a permanent advertisement sign.