leaking poptop roof

Hi Chris,
Don't know if it is still available but there used to be a produce called "Wastolan".
It was a plastic/rubber product used for painting/spraying onto grain silo's to seal them for weevil fumigation. The whole silo was painted.
Was available only in white. As with all paint type jobs the secret of a successful job was in the preparation.

Another thought,
There is/was an underbody rubberised paint called "Schust" or similar sounding name. This was sprayed inside mudguards and along the panel below the doors to protect from water. This was available in a number of colours. Should work.

One very big hint:- If you are planning to spray or brush paint your van roof, set up a couple of very stable trestles, one on each side of the van and put a long wide plank between them, high enough to drive the van under, and paint the roof from there. Caravan roofs are notorious for creating more leaks than you fix, if you are putting any pressure on the roof.

Good Luck

Disco.