Same happened on a 22FB I had. Use #8 stainless oval head machine screws, SS finishing washers, SS flat washers and Nylon lock nuts. Through bolt it putting the screw heads and finishing washers on the outside because they will look the nicest showing, use a flat washer and lock nut on the inside. Cut the screw off flush with the locknut and smooth with a file so it doesn't hurt the seat back cushion.
If you are using the dinette for a bed, I would also through-bolt the support strips on the front of the seats because they are also going to come off.
While you're at it,look around for anything that may come loose under stress and screw and glue it together using a good wood glue. The staples used to build these trailers are a joke.
2013 F250 XLT
I now have a Keystone Outback, but I try to help when I can.
Bitter Gun Owner