Hi all ,any thoughts please.

Recently had a habitation check on a Bessacar e 530.on the report it came up with 69 percent in rear corner ,on plan it looks like behind toilet in short ,to fix!!!!!!! cost was £2800 ,less £1000 for warranty £1800.This includes removing rear bumpers ,wall panel etc making good .Removing toilet
Have today with small damp meter checked and then a near by caravan dealer checked and none of levels show any causes for concern.
Having spoken to MH dealer it appears that the damp is on underside of floor ,have checked under van myself and yes right at rear of van levels are higher ,there is no damage to floor and black bitumen is in tack.Dealer has now agreed to recheck this area .Also levels much lower in middle of floor pan .
My question to you all is the van is parked so most of rain runs of on this side of van at rear ,also it on offside behind rear wheels taking all the spray.Is it likely rear walls need to be removed ,is it normal for higher level of damp in this area ,it is as far back as spray could go