I did mine last weekend and followed So-Kal's advice and used Martrim's brushable contact adhesive, I used a couple of spreaders rather than a brush though and it was really easy to use. According to So-Kal, who knows a thing or three about car trimming, the brushable contact adhesive will hold the carpet better and for longer, so it won't start peeling in a year or two, plus it's only a tenner for a one litre can, which is more than enough to do your whole van. Bargain.