I’ve been unlucky and experienced this bubbling problem on two vehicles. I experienced it on my first Marco Polo - a Marco Polo Horizon - the body shop on inspection ordered another roof. I actually changed to a new Marco Polo before the work was ever carried out, but Mercedes impressed me with this solution rather than wanting to paint the problem.
My other experience was with a Niesmann+Bischoff motorhome. The Hymer groups solution was to strip and respray all the effected areas which was every bit of fibre glass.(bonnet, wheel arches, rear panel) They did this at their expense. The solution didn’t solve the problem as bubbles reappeared. The second time they didn’t want to accept any responsibility (warrant lapse) but in the end they paid half of the £8500 bill to do the work again.
What I’ve learned during these episodes is the problem occurs when the fibre glass isn‘t left to breath/lose moisture for long enough before its painted and put onto your vehicle. I’m not sure if it can be sorted by stripping, re-prepairing, and re-painting. The problem for me on both vehicles happened over the winter I think caused by frosts. The bubbles actually reduce in size in the summer.
I think worryingly for all of us these problems are well known by our manufacturers, they are caused by problems in their manufacturing processes. They understand the causes but are very reluctant to share what they know (to limit liability)Presumably they can identify possibly effected batches, but they do not do recalls. And finally sadly if enough time goes by they don’t want to deal with the problems at all (because of cost)
Its worth inspecting your vehicle as we come out of the winter as the sooner you start the complaint process the more likely your going to get help and a solution.