Finished and tested my latest diy project. Used a 44gallon Brute garbage can on casters. Sized for up to 3 corny kegs.
I used no insulation around the perimeter of the can but insulated the top and tower. Reinforced the top with a circle of 1/4" plexiglass. It was tested last weekend and held ice for about 8 hours in shaded, 85deg heat. Taps were sweating the entire time. Used a Kobalt portable CO2 regulator with paintball tank to push the beer. If I decide that I need better performance I may drop this into a 55gallon brute and use a two-part, pour-in, insulation in the gap.