JimK-NY wrote:
I think you are close to a solution. That angle bracket looks good especially if you include some structural steel from one side of the camper to the other. You could also consider extending that metal plate higher on the side of the camper, maybe even a foot or so higher than the jacks on the wall of the camper. The more, the better.
The angle iron will strengthen the side-to-side support, but perhaps you also need more support for the jacks and brackets in the front to back direction. Maybe another angle iron welded on at right angles to the one you are planning to use. Even better perhaps 2 pieces of steel going front to back. One piece should be toward the top of the bracket and the other as low as possible.
Perhaps I have not described this well. What I envision is a cradle under the camper so the lifting is on the cradle not on the attachments to the camper.
https://www.truckcampermagazine.com/camper-mods/contests/truck-camper-exoskeleton/