My white caravan roof has a seam running down its centreline. The seam is covered by a beading which I assume is PVC. The roof is painted aluminium. The caravan manufacturer (Jayco) has used an opaque white sealant to cover the edges of the beading however I don't know what that sealant is. The roof has started to leak when exposed to heavy rain and I am 99% sure it is a result of the puddling that occurs on the roof around the beading. Puddling is difficult to avoid as the caravan has to be level when occupied. The caravan is usually kept under a cover when at home.
Selleys Solar Flex is going to be ideal for this application. If it is a silicone sealant that has been used previously it could prevent the Solar Flex from bonding properly, so you will need to completely remove or scrape off the silicone before applying the Solar Flex. Our Silicone Remover can be used in removing the silicone.