try a local caravan place or b&q find out were damp is coming from (i.e) door window and do what you can if its window put some clear sillicon rouned it
25mm wall boards should be available at a good builders merchants, use the foam type as it doesn't hold moisture.
For damp use some creeping crack cure, but first you will need to find leak. Silicon sealant could also be used.
No idea where to get it from, I don't live anywhere near.