Three years ago I bought a 2nd hand 92 Jurgens Palma, and have had it for 3 years now. I have been looking at the sealant on the van and it does not look to good. It has starting to peal in places and has gone very black with dirt. The van is housed under cover and is not subjected to the elements, except when camping. I have been considering having this redone as I am not sure if the van had been resealed correctly by the previous owner. The caravan is also due for another service.
Your query and Mark's response, prompted me to phone a caravan repair shop on the West Rand. I was quoted R980 for the removal and resealing of the whole caravan, including the pop-up.
From Mark's response, this does not appear to be a "do it yourself" job and I cannot see myself tackling this type of job on my own.
I have decided to have this done, in the next month or two prior to my next trip. A caravan is an expensive item, and does need some attention from time to time. The cost justifies the time and effort and in addition the work carries a guarantee.
I will be happy to to supply you with more details should you require.