Have been considering for a while in investing in a damp meter for obvious reasons.
The Protimeter is the bees knees one evidently but it comes at a price,round about £180-£200+.
I bid for a couple of Protimeter Minis on E-Bay but didn't win.
I then stumbled across some much cheaper meters,also on E-Bay :-
Cheap Damp Meters
Bought one of these for £6.99 including batteries and free postage:-
Now I don't suppose it is all singing and dancing like the Protimeter but it certainly does the job,including ambient temperture readings, and is about £170 cheaper,the only slight drawback I have discovered is that it doesn't "hold" the reading so you have to look at it while it is stuck into the wood which is hands and knees job when doing the floor under the van ( which along with the inside floor is the only place you can check on an Alu-Tech van the walls being GRP coated ).
Will now be entering compulsive/obsessive mode.