+1.
I'm not a fan of luggin buckets, but neither do I have the luxury of a mixing station. So I recommend either the 35 gal action packer totes (Rubbermaid brand is cheap but good) or a Plano box (bullet proof but $$). If you drive like a maniac the Remington totes tops are water sealed.
Either way, 6 5-gals will get tiring over time so I'd make a wagon. Buy a 30 gal (or two 15), affix it to a dolly and make a wagon.