Out of town for a few days. I will try to get some photos with dimensions soon. I'm always behind on something
I made my frames out of 3/4" thick lumber and cut a groove on the inside that was about 2 saw kerfs wide to hold/support the pierco foundation. I used deep pierco foundation for the jumbo frames. I used 1 full piece and cut another full piece in about half to achieve my jumbo size. I must say, it was a pain in the butt to match up pieces of plastic foundation! It would be great if piecro or somebody else offered their plastic in larger sheets that we could simply cut from. I haven't checked around. It would be great to know if somebody does find a source.
You could just use 1 deep sheet of foundation in a jumbo frame and let the bees build the remaining space freehand. However that will probably result in a bunch of drone comb and quite likely crisscrossed too. I think I would avoid foundationless when working with such large combs.
The piecro foundation does result in what I would call normal sized bees. If you make your jumbo setups based on small cells you could go with smaller frames and still have just as many bees per frame and 1 box for brood.