One word: Durock. Explanation: cement board normally used for vertical installs of tile, etc., especially in wet environments like showers. It is also heat-resistant and would ensure no heat transfer from the legs to the elevated surface where you are cooking. It’s heavy so you’ll want to size it to meet your needs with no excess.
Durock. Good new word. I watched the video. Do you think Home Depot will cut it to size for me? And can I keep it outside?
https://www.homedepot.com/p/DUROCK-Next-Gen-1-2-in-x-3-ft-x-5-ft-Cement-Board-172965/202263276