OK, found my main problem...
My door has a gas shock at the bottom to hold it open, in case of wind, or whatever. We are parked at an RV park in Dalhart, TX on our way to Colorado, and a similar model pulls up next to me, and his door has no shock but a latch that catches when it is open, to hold it open so wind won't slam it back and forth.
So I pulled off my shock, and here is what happened...
FWIW--I noticed I was starting to see light at the bottom hinge of my door a couple weeks back. This will fix that, as well as the slamming.
With shock installed, it was pushing the bottom of the door about 3/8" against the door frame.
With the shock off, the door squared up and there was an equal gap all along the leading edge of the door. No longer hitting at the bottom, and no longer hitting the striker at an odd angle.
Also. The screws holding the striker are already stripped, so I need to put new ones in, and make that thing stop moving around.
Shock is off, door closes MUCH easier now. I need to buy one of those flip-over latches to hold the door open, now, like my neighbors.
I also need to glue or screw or something to keep the door square, and to fix the broken attachment at the bottom corner of the door that the shock caused.
Any suggestions on what would work better to hold that corner together?