I don't know of any kind of mounting plates. I'd say Carl is in the best position to comment on this. I wouldn't recommend installing a ladder unless you have a walk on roof, which I don't think you do since I think the ladders came automatically with the walk on roof option.
Kitty, I don't see why a window awning would be too much trouble. On the coaches I've see with those added, I've seen the rail mounted just above the window frame so it should hook on the stud. I think the mounting of the arms would be the difficult part. I suppose you could always pull aluminum off and put some new studding in there to support the arms, but that's a really major job.
Another option would be to drill four holes right though to the inside and get some really long lag bolts. Put the bolts through the holes on the arm bracket. Drill the hole inside a lot bigger, about 3/4" or so, to allow a dowel to go in there. Get a good size dowel rod that you can drill a hole through the center and cut it to the width of the wall. Put the dowel on the bolt inside the wall. Cut a slot in the hole to allow you to put a bigger washer in there. Put the washer on the end of the dowel and put another big washer and nut on the very inside to cover everything up. This should allow you to tighten it up very tight and still support the arm. Put plenty of putty tape on the part going up against the aluminum. It would probably be a good idea to paint that inside washer/nut to match the paneling/wallpaper so it won't stand out as much. Repeat these steps for all four bolts. I only recommend this method because the nuts will probably be hidden behind your couch anyway. BTW, if the bolts will stick out somewhat far, I'd recommend cutting them off before you do the install so you and/or the couch wouldn't catch on it.
2007 T-286SR Cherry/Granola, #6236, original owner, current mileage: 9467.8 (as of 5/26/19)
1997 T-2653 Blue Denim, #5471
1979 12 1/2' MC, Beige & Avocado, #4639
Past Sunlines: '97 T-2653 #5089, '94 T-2251, '86 T-1550, '94 T-2363, '98 T-270SR