We've just bought a VERY cheap caravan to use as a tack/tea room. It definitely won't be going anywhere else unless it's the scrapheap in the sky, it's a 1988 (?) swift corniche 12/2 if that makes any difference. There are 2 spots on the sides at the front (near the windows) that are soft, we've identified a likely hole and filled it and will reseal the whole van. Apart from that I'm not interested in ripping it out to repair or anything, the rest of the van seems solid enough although I'm not going to go overboard investigating, so my question is, if this was yours what would you do? Seal the outside and leave/ignore the soft spots, or is there some type of glue that could be painted on to bind the patches together a bit just to make sure they don't crumble then restick the wallpaper? They're not massive patches I just don't want them to get worse and it would be good if we could get a year or two out of it just sat where we've parked it!
I've a reputation as a bit of a bodge it numpty.
If it were mine under the conditions you describe I'd look at rubbing down the front panels and repainting them with a couple of thick coats of waterproof mastic style paint.
In this weather leaving it open to air will help it dry out a bit.
A common problem and one I have recently encountered in our 1992 Elddis which we do hope to get a few more years out of.
The damage is almost certainly much worse than it appears as I only found a couple of soft patches to start with. It turned out the entire front end was rotten, but I had half expected that.
As you are not expecting to use yours in the same way that we are, I would just seal up the outside, let the interior dry out thoroughly, then stick some panels over it. You could use something like very thin ply, sticking it on with an adhesive such as grip-fil.
I have had to make up all new framework and cut out wooden ply panels as a replacement. It hasn't cost much, less than £200 including a step-platform costing around £60 to get at the outside, but it is very time consuming. It should buy us a few more years with it though, and we plan to go away with it again later this year when it is finished.