I think bubbles between the plywood roof and the rubber membrane happen very frequently. They are a defect, a failure between glue and plywood or membrane. Manufactures have seen it enough that they "determine" that a certain amount (nearly all) is acceptable and does not affect the membrane performance. In my industry, we'd establish a maximum acceptable defect size, spacing, and other criteria to accept or reject defects. I'd love to hear a Travel Trailer manufactures criteria. With no published criteria, it is easy for them to say "that is normal".
I wouldn't use the word normal. In this context, the manufacture is saying it is not a failure. When they really should be saying "this type of failure is acceptable since it doesn't affect performance".
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Tom
2017 RAM 1500 4x4 5.7 HEMI
2015 PCW ECON 18RBS
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