I saw a boot post on the FB site and wanted to share my solution here.
I used a product called Sika Post Fix bought at the Home Depot. It's an expanding foam used to fill post holes instead of using concrete. This shit is strong!! I have a 1/2 ply wood base, nothing inside the boot, and it holds my 270+ lbs. Best part is it weighs less than 2kg per boot. I can dance in these, lol
I built the boot shell and affixed the plywood to the bottom. Then "mixed" the Sika post fix and poured it into both boots. You need to work quickly because it sets and expands fast!. Once it stopped expanding, I cut the tops flat and added a 1/4inch piece of cheap wood on top. Initially I used screws but they pulled out so I used long bolts to secure the top to the bottom, and then screwed the shoes to the top piece.