I used Insul brite, cotton batting, and canvas cotton cover when I converted a wooden tv tray table to a mini portable ironing board. I plan to add a wool pressing mat to mine, (one day when I re-cover mine), and will just put it on top of the batting and underneath the cover. I don't use steam but even if I did, I don't think the steam would reach the wood of the tray through all those layers.
here is a link to how to do this. Also Missouri star did a you tube video on making an ironing board out of a tv tray and she used elastic on the cotton cover instead of stapling.
I love mine and have used it for about 8 or 9 years. Bought the tray table at a thrift store for $5.00. Perfect for retreats and workshops.
https://www.youtube.com/watch?v=XHpzQ3_fqxM
https://blog.american-quilting.com/?p=1908