I've used large diameter ABS pipe cut into various sized sections to support some of my LR. Holes in the sides will allow some movement & help mitigate stagnation in the sand bed. If I were to re scape, I would do similar, but instead of rounds with holes, I'd open the circles up into half or 3/4 sections. I'd also silicone them to the bottom, since keeping them in place was a pain while trying to place the rock on them. I didn't know ABS has a tendency to float. Not an issue in your case since you'll be working with a dry tank.
Something like this, but clean up the edges of course:
Not sure I'm a fan of the eggrate scenario, since the latticework would seem to have the tendency to restrict flow & sand movement within the individual squares?