safe bottom paint time

[ebb]

Speaking thru my hat.
What I know is this from a safety standpoint:
(probably the single most important thing to know about epoxy)
Use 100% solids epoxy of one to one or two to one A to B parts.
100% solids epoxy is relatively benign.

Simple, do not use any manufacturer's formulation that has solvents in it.
Do not use any manufacturer's product that blushes.
That includes your favorites: East System and System Four, N.A.S.
Blushing is an indication of cheap extenders like nonylphenol (a carcinogen).
Extenders are a way of cheating the consumer.

The only reason not to use epoxy on foamboards is the expense.

One very good reason not to use polyester on boards is the styrene solvent in it. In 1982 A USEPA study found styrene in human fat tissue in 100% of the people tested. Causes liver kidney brain and lung damage. Styrene also rearranges your chromosomes.

(Why won't epoxy stick to urethane foam?
It's not compatible with polyethylene and polypropylene.)