Loading up slide on camper.

forgot to add, grab some of that tape and stick some on the rear of the slideon where the tray should appear and check that it lines up, now the tray should line up with both bits of tape and you know it is square.
Took me some frustration to get it right but now can do it within a couple of mm in 2 or 3 attempts.
If you get some one to help you you can push on the side of the slideon while lowering it to get it in the perfect position