When the temperatures are reasonable I pour directly from the mix container onto the boat. When it's warm enough to make the epoxy kick quickly I use a tray as that delays the reaction.

Laszlo

   If it's really hot, I keep the epoxy cool in an ice chest or fridge, mix it then pour into a metal cookie sheet that I keep cool also. That's the only way I've been able to work epoxy in hot Florida summers

I've not had to contend with high temps too much in my build but the cookiesheet idea's a good one if you're challenged by heat. I did buy a few cheapish plastic storage boxes with lids before beginning my hull's encapsulation. The lids worked very nicely as flat trays for epoxy, weith the added bonus that the hardened epoxy left behind can easily be removed once it's cured hard enough to peel off. I doubt that would be possible off cookiesheets unless maybe the Teflon-coated kind.

Choose your roller covers wisely! Those meant for paint likely will leave fibers behind if they don't also begin to pull free of their cores. The thin foam rollers from CLC and elsewhere work well though I did encounter having the foam begin to pull away from their cores a few times.

I just used some covers meant for epoxy coating floors for coating my spars. They bear a woven 1/4" fabric layer on a plastic-like core and seem to work well. They leave a thicker layer of epoxy than the foam rollers I've used if that's of value. Being sold in hardware stores they're a good alternate if you run out of others bought on-line.

Lastly be aware that the higher volume of mixed epoxy held in rollers' coverings will tend to accellerate heat of reaction generation. You may find your roller begins to drag while the epoxy you're rolling out is still fairly liquid so plan ahead, don't mix up more than you think you'll be able to apply in the limited time required before it begins to kick off.

   I usually mix up 6-7 pumps at a time and dump it on the area I'm going to coat. Then roll it out with a foam roller and tip with a foam brush