I may be the one misunderstanding the OP's request, but I thought he
was asking about 2 part epoxy - Paint - not laminating resin. If so
there isn't much that can be done about extending the shelf life once
the hardner has been opened. Maybe blow some argon from the TIG in
the can and do the same with a zip-lock bag around it for storage?

The last place to store it is in the fridge with food. (been there,
done that, and the fridge made the food taste strange for more than a
year) The stuff reacts with moisture and the innards of a fridge is a
very moist place.
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Leon McAtee