I bought a new to me TT that is in really great shape and had very few areas of de-lamination. I noticed that the dealer the folks I bought it from who they got the unit from a year ago, went over it ...
This is the leak test rig that I built using a blower from Harbor Freight and a concrete form from Lowes:
The form is fitted into a piece of cardboard I cut out to fit the baggage door. I sealed it with duct tape. Make sure all your vents are closed and lock the range vent for maximum pressure.