I recently did some work on our camper (framed/filon). Ours does have internal backing plates as most framed campers do. Its a piece of angle. There are lag bolts into frame but also bolts that go all the way thru. I had to remove both front jacks-I can see the backup angle on slide side and noted nuts were welded so happily removed jack plates-last bolt on slide side the back up angle started to move. So I ran a bolt back in thru hole on jack plate that was removed to hold back up in place. Was glad that nuts were welded cause I couldnt get to them-but kind pointless if whole back up falls inside.
Drivers side when I went to remove the nuts werent welded just spun. Ended up pulling water heater. Though the nuts werent welded the angle was screwed to wall? Go figure..
Point is if you or someone cant verify that back up is anchored or integral (embedded to F/G?) could remove one of the lags use a smaller head screw the jack hole will pass by? Or a much longer lag so you can partially pull plate and then insert short lag behind before fully removing.
