Hey rickwagon,
I made my own jack brackets during my build, as you can see by the link below. I had some older corner jacks that originally had bands around the tubes that tightened down when installed. Instead I decided to weld some mounting plates to the top of the jack tube, and then I measured and drilled three holes equally spaced. On the camper mounting brackets, I used aluminum flat stock and angle stock to form the bracket, and drilled holes to match those on the plate welded to the jack tube. To install I bolted the flat and angle stock together and installed with three inch lag screws, after applying butyl tape to the inside surface of the bracket.
If I were to do these brackets again, I would either go with thicker aluminum (1/8”), or possibly stainless steal, as mine are a little more flimsy than I would like, nonetheless they have held up and worked pretty good so far.
Hope this will help. You can scroll up and down on my build thread for anything else of interest. Good luck!
Poky
https://www.wanderthewest.com/forum/topic/12116-full-build-reconstructing-a-1981-grandby-into-a-custom-hawk/page-5