if a shop did that type of work(false floor, box) its horrible, if you did that its a difirent story . Jetta if the fiberglass is cracking if could be many things(they "winged" the mekp, got cheap resin, old resin) a lot of times installer will make fiberglass, paint it fine, later on mat will show through resin, it will start cracking, become brittle over time etc. Watch out man keep a eye and ear out for that CUSTOM FIBERGLASS SPARE WHEEL enclosure i got a feeling thats not the end of youre fiberglass nightmare.