Checking for damp is fairly straight forward; the best way is to use a damp meter.

Another way (though it will not show the early signs of damp) is to use your fingertips and press hard against the wall board surface , if you feel any softness then there is (or has been) damp underneath.

Wall board softness means that there has been water ingress for some time.
Other indications of damp are staining on wall boards.

You should check the entire caravan, under cupboards, behind seats, around windows, in corners, the ceiling - everywhere.

Damp Meters.

You can buy cheap meters from places like B&Q, Screw Fix, eBay etc.

Cheap meters do give an indication of how bad the damp is by the amount of noise they make.
 A ticking sound means slight moisture, where as a high pitched scream means excessive damp.

When using damp meters the probes need to penetrate the surface of the wall board to get a proper reading. I sharpened the probes on my B&Q meter using a file.  The probes are now needle sharp.


Some meters are called Protimeters, these meters are far better at detecting how much damp is there, i have bought the yellow one shown in the picture below, well worth the money ( bought from Ebay for £50 ) . 

These types of meter show how much damp is present with either a digital read-out or a colour scale.

Readings between (0-15%):   no cause for concern.

Readings between (15-20%):   dealer to make a note of these readings and re-check at next service.

Readings between (20-24%):   possible early signs of ingress. Look for tangible evidence or ask for a re-check.

Readings between (25-30%):   moisture evident, remedial work required; may not need strip-down unless surface damage (staining, pimpling, and softness) is apparent. (There is a risk of wallboard deterioration due to retained moisture in the structure if resealed only.)

Reading (31 % and above):   structural damage is occurring, deterioration inevitable. A full strip-down of the affected area is required.

Protimeter