Understandable. You don't have to build a collar with a keezer by the way. I have a 2 tap tower mounted to the top of mine reinforced by a 2x8 that I sunk in the insulation. I have 2 kegs, a pc fan box/blower, 5lb CO2 tank, and a carboy that I am lagering in there right now. I think it is a 7.0 cu ft. I hear ya on the portability thing but it might be worth looking into, especially for the extra room to expand or lager if you want to.
"Offered a Bud Light, and a glass of water - I'd drink the water. You only have one liver, don't waste it on bad beer." - Brock Wagner