Bubbles are usually caused by heat from the outside or moisture on the inside. By any chance does your bay door cover the furnace or water heater when opened? Both of those vent a lot of heat and can damage anything too close.
Otherwise, I would suspect a water leak around the edge somewhere, or maybe where a hinge or latch attaches.
The only repair technique I know requires slitting the bubble open, injecting a glue underneath and clamping it flat until the glue dries. You will probably have to trim the edges back a bit because the laminate likely has stretched a bit. If you are very, very carefrul, you can get the edges of the slit to join nicely. If not, repair the remaining gap with a fiberglass gel coat repair product, usually available in boat stores. Of course, you could always cut the entire bubble away and fill with a fiberglass patch, then paint the bay to match the coach.
Former owner of 2004 American Tradition and several other RVs
Home is in the Ocala Nat'l Forest near Ocala, FL
Summers in Black Mountain, NC