Do not mixup enough epoxy to cover the boat. Epoxy curing is an exothermic, generates heat, reaction and will cause gas bubbles to appear in the mix and accelerate the curing of the mixed up epoxy.    

You might want to review the Working with Epoxy and Fiberglass articles, especially the Conserving Epoxy and Fiberglassing. It is suggest that you work with a pint at time Also have enough time to work the length of the boat so either the inside or outside is fully covered before ending work for the day or for a rest.

To add to what George said . . . mix in small batches and in shallow dishes. The stuff can harden fast if you don't get it spread out quickly. 

I once mixed up a fairly big batch of epoxy for fillets (maybe 10 ounces in a plastic bag, like a big softball). I got distracted for a few minutes, and when I came back, it was steaming and too hot to touch! And, of course, too hard to use.