Ooops! Now to fix it ...

No need for all that heavy hardware! As one of the videos I posted shows, all she needs is one of these, available in every hardware store in the country in various sizes:

Have you tried using a bottle jack wedged between a 2x4 on the RV side and a sturdy object on the other such as the lamppost idea or a big sturdy tree. With the jack you can observe what's happening and hopefully it will pop back in.

Perhaps you should use what are called "fender washers" which are large but have a small hole in the center. Less chance of pulling through or making an ugly repair with wavy sheet metal.

This might sound a little "Out There" but you might want to try this.

1) Find a parking lot with a solid concrete lamp-post base.
2) Place properly sized lumber between the concrete and the place on your low-point rear wall where it pulled away.
3) Very slowly have your spouse or friend back up the rig while you hold the lumber in the right place for the right pressure point. Some practicing on extremely slow backing would be a good idea.

Let the rig creep extremely slowly without using the gas pedal until you see the separation start to close. It might just go back into the right position once relaxed. Then caulk and I'd think you are good as new.

Or you could just wedge a 2x4 between the bumper and the corner and pry it. Much easier, and safer.

Hi jillhop, BUMMER on the corner. I did the same thing to the moulding on therear streetside pulling out of a bay at the local quick oil change place. Kinda tight area, didn't pull out far enough and the swing of the backend caought a concrete thing at the door entrance. My fix. I drilled a hole in the moulding and put a long stainless steel screw through it to pull it up tihgt and then calulked it. Can't tell any difference from the other side.
Good luck.
Life is a trip, ENJOY the ride.
Safe Travels.

Caulk is good for now but in the spring you might try eternabond. Here is a photo of our rear corner repair.

I took off the metal trim to the top but let it hang, then used 2 2" strips of eternabond overlapping the corner then rescrewed the trim using new stainless screws and replaced the vinyl strip.

Another way to put pressure on to straighten or hold a glue joint is to use a scissor jack, you might have a couple to stabilize the RV when parked.
Ours were brand new here. We used the car to secure against because it was the right height. Here I was gluing the filon back on a lower area repair.

Good choice, Darned leaks are so hard to find at times

Thanks for all the suggestions--very helpful! Since I had the ProFlex out today anyway trying to stop a leak, I just put some in the gap and sealed the area for now. The mobile RV tech is planning a visit in the near future, so I'll have him address it more permanently. I'm confident for now that water won't be getting in (at least not there ...). :-)

Some youtube ideas:

https://www.youtube.com/watch?v=ms2ba79OvRM

https://www.youtube.com/watch?v=Re19I08pvAQ

Does the rear side have a vinyl insert? If so... Pull it out from the bottom. This should expose the heads of screws which have pulled away from the body. You can try to rescrew them, or try longer screws. Most likely the best way will be to redrill the screws into new holes away from the existing ones.

If it has the screws I'm talking about, the right way to do this includes getting some putty tape and applying it under the trim piece. Afterwards, it still would make sense to use some Proflex RV caulk or similar product on the upward facing lip of the trim piece.

In a pinch for now, buy some GOOD foil HVAC tape. It is great stuff. You can tape the edge into place with it, and maybe a dab of caulk on the top edge of the tape where it starts.

A mobile RV repair service could probably fix you up in 15 minutes.