running a dehumidifier to make a swamp cooler work is a losing proposition no matter where you try it, the heat the dehumidifier makes would cancel out and probably override any cooling youd get from the swamp cooler. a swamp cooler ONLY works if your rh is under 40% or so, and the lower the better. if the rh in your shop is under 40% it would work, if not, then no. and no amount of dehumidifiers is ever going to make it work properly. ever. anywhere.
if i realized it, i would, indeed, know shit. i have short hair, i take a shower, and using a dehuie to make a swamp cooler work is a goofy waste of time and electricity, if you want to waste electricity, knock yourself out