Yes they will and yes it is.
I had to pay 25% of the repairs to my van because of a late first service (my fault that as I had other issues going on in life)
I believe it was about £380 so full price would have been about £1500, it's the labour you paying for.
Discounted Insurance Quotes for UKCampsite.co.uk visitors! Up to 12.5% off!
You can buy a Stanley damp metre from b and q for £40 and they are accurate, more so than really cheap ones but not as expensive as a protimetre. Or you can hire a damp metre from a tool hire shop.
I wouldn't buy at any price without a damp check.
One other thing that so many people miss, take some step ladders and have a good look at the roof, just in case of any damage that you can't see at ground level.