Having played with epoxy for many years....
Don't tie up more than you will use THIS SEASON... Virtually every epoxy "mix" (meaning 2-part) I have tried turns brown within a year... I no longer use it very often.
If you are using it to place a drop on the wing-case I find a strip of flash works better.
SOFTEX is a product I use to coat the bodies of some flies; like my cord-body bunny flies.
SOFTEX remains pliable, is durable and it doesn't yellow or turn brown with age. I recently gave some of these flies to TROUTMAN that were tied several years ago and they looked brand-new.
SOFTEX will also get you stoned unless used in a well ventilated area; I do it outdoors. HUFFERS would love it... LRO may have it; ORVIS sells it.