Damp meter use

Flutel

I have just bought a damp meter to check damp levels in my 18 month old caravan. The service revealed high levels (beginning of April).  I have duly left it for a good 3 months before it is re-checked. My damp meter has two prongs that the instructions
tell me to stick into the surface for 5mm.  Is this ok to do in a fairly new van?  I will be sticking it in the back kitchen/bathroom bit.