We have an extremely nice 550 for sale. $17,000 or BO.
It has;
Electric Brakes
AutowBrake Brake Controller w remote (no need to add a controller to your tow vehicle)
SUV Off Road tire and suspension package
AC
Mahogany Interior
Grab bars above doors (handy!)
Newer AGM battery upgrade
6000...
You can remove the outside handle by taking the two phillips screws out of the outer escutcheon. The handle then pulls out and you can work on it. As others have said, the inside locking lever might be the issue if it is pushed to 'lock'. Have you tried jiggling the handle whilst turning the key?
We don't use our CI AC very often. But when we do, it is really appreciated. We usually use the teardrop after Labor Day, but every trip it seems, we encounter at least one day where either the heat or humidity is very uncomfortable. We are in MN.
Screw a big eye bolt in the back of the garage, then use the item below to pull the trailer in slowly, while a helper steers the tongue end. I have one of these and it is amazing...