I have done a fair amount of experimentation with acrylic fuming boxes, but I wouldn’t recommend acrylic gesso on wood as a substitute. You would be pretty much in the “unknown zone” with the various ingredients in gesso, and I strongly doubt any paint layer would reliably protect a wood box for very long. I’m willing to be corrected by someone who has tried this, but I wouldn’t go there myself.
It really isn’t all that hard to grind a Pyrex dish lip flat and prepare a ground glass to cover it. Enclose that in a wood box and you have a time proven and safe container. See the Resource page for images of various types.
As for displaying iodine, any lab supply company can sell you a glass jar with an HDPE cap and a PTFE (Teflon) liner that will contain iodine adequately for a display. If the glass stays intact, the iodine – both gaseous and solid will be contained.