Welcome to the world of vintage caravanning cgl80. Consider finding a leak before you've gone away and blessing! Where the water is pooling may NOT be where it's actually getting, because it could be running from a totally unrelated area. It becomes a matter of trial and error. I would start with the J or right angle shaped cover strip where the wall and roof panels meet. Remove, get rid of whatever sealant is there and reseal. Do the same over top of the windows. Don't put new sealant on top of old. Trial that with a pressure cleaner.
The problem you have taking this "short-cut" method is that you won't know how much damage the water has already caused. If there's wood-rot, it may continue to rot! The optimum is to carefully remove not only the cover strips, but also any panels around where you can see the water puddling. Your framing may already be rotted away. What you see from that will dictate where to from there.
As a departed member of this forum used to say - it's all fun!!
That’s the thing, there isn’t any external cladding. The side walls are wood. There is essentially only 1 layer. The only thing I can think o dis where the sides meet the aluminium. And it doesn’t have j-rails like typical vans either, because the sides are wood.