I was thinking that squares cut from 2x2 lumber might be more stable than corks, for supporting a cap mat plus cells or pots.
Also, I've been looking for cheap, deep, cheap, sturdy cheap trays. Dollar store cat litter boxes come closest. But they never fit 1020 - sized plug trays or inserts.
I finally realized that I don't need them to be 12"x22" (or whatever). I always cut my prop trays and inserts into manageable sizes, like 1/3rd or 1/5th of a 1020 tray. Then I can sow all one varioety in one "segment" and move it to another tray with no dome or humidity film when it emerges.