Hi Huckleberry,
I don’t think there is any information or consensus available anywhere about “how much” ventilation would be needed in specific situations or with different mattresses or the balance between support surface and airflow or even a way to measure it objectively so it would be more a “best judgement” situation depending on the other risk factors that may affect the moisture retention of your mattress and the risk of mold, mildew, and dust mites (see post #10 here).
I have no experience with the bed you have but in looking at the animated instructions it seems to me that it would be strong enough and drilling holes in the masonite should probably work fine for ventilation.
Phoenix