Damp

I wouldn't buy anything with damp at all. In fact run a mile. Quite a few, Baileys suffer from water ingress from the roof strap,  which then works it's way through the walls and rots the floor.

Best to get an independent inspection ahead of purchase if in doubt. 

Buy a dry caravan with good service history from a dealership  - at least you then have some comeback under the consumer right Act 2015 if they sell you a dud.And pay at least ~£1K on credit card for added useful protection 

If buying privately there is no comeback - it's buyer beware i'm afraid. 

Damp is the worst as much of problem could be hidden.......

Yes, 33% is bad. Up to 15% is normal. Check out THIS link.

Btw, it’s £100 on a credit card to get protection. Search online for Section 75 credit card protection if you’re interested.

Whilst it could be the roof strap - a more likely source is the shower tray. The Bailey shower tray is quite flimsy - and not supported at the edges where it's sealed to the shower walls with silicone.  With use and movement, that seal eventually breaks down and all it takes is a barely noticeable hairline crack in the silicone - and that's enough. It happened twice to our Barcelona (2015) within three years of getting it.  The second time, the whole bathroom had to be stripped out to remove the floor covering to allow it to dry out. On that second occasion, the highest damp readings (about 40%) were around the base of the toilet.