Well, it's fixed.
Thanks to everyone for their suggestions. I tried the simple solutions first - pressure on the door, moving the trailer, bottle jack under the frame - no luck. The latch would not retract. Door hinges not accessable, slide outs open, so I had to fix it myself, on site (AAA does not do "repairs" on lock assemblies, only work on the locks themselves, which were working fine). With all windows locked and no access from beneath the unit, my options were to break a window to gain access, or to try and demo the lock. If it had been an emergency, breaking the window was the obvious solution, but since I had time, and since the lock needed to be replaced and the window didn't, I went to work on the lock assembly.
The suggestion to "hog" out the screws was not feasible because of the contours of the casting, so I used a pipe wrench and a claw hammer to break the handle off to get access to the plate covering the mechanism. Using a punch and a cold chisel, I managed to get access to the latch and pull it out (my Dremel tool was not powerful enough to use on the casting), but all the pounding had now rattled the deadbolt loose from its lock, and it had moved into the frame! Another 20 minutes of hacking away at the casting and I was able to hook the deadbolt with a piece of coathanger and open the door.
In the future, I will make sure a least one window remains unlocked for access! And although my $95 replacement assembly seems to be of better quality than the original, we will be much more aware of our actions when entering and leaving the trailer - no more slamming the door!
Thx,
Ken