Hi, I believe the Thorn Adventure has a sealed frame, apart from the seat tube. That's what it says in the blurb, anyway. I used waxoyl to seal my bike frames, although it's not ideal as it never set and kept dripping out of the bottom bracket for ages. It was tricky to guage how thickly it was applied, using a spray tube attachment. I have heard that Roberts supply some sort of frame protective, possibly Wiegles. Thorn may do something also.
Have a good adventure on your Adventure!