Hmmm...interesting addition on using the Prime, SH03 - that isn't the blue stuff, is it...
I've got a half dozen eels left I've had for a week under bubbleweed using the 3 bucket system, forgot about 'em under the deck and checked 'em yesterday - still alive & kicking. Forgot to ice them for 2 days - of course, the cool rainy weather helped
The big trick I found using my 150 qt cooler for more than a dozen was putting in 2 frozen gallon jugs of water to keep the temp down to the low 40's - slows their metabolism waaay down and the colder water holds more oxygen - just use one of my old aquarium thermometers to check it pretty regularly
Definitely gonna try that Prime stuff, though - I would guess you can pick it up at an aquarium store.