As Bluesman suggests, the best way is to make cut outs & try it. Most of those freezers have a little shelf over the compressor that can't hold a 5 gal corny, but can hold a blow-off bucket or a 2.5-3 gal corny. You simply plug the controller into the wall outlet, set the desired temp & then plug the freezer into the controller. The probe is a thin wire that can just slip under the gasket of the lid.
Search the forum index for freezer conversions (or keezer conversions) and you'll see a lot of folks build a wood collar that sits between the freezer & the lid. You can drill through that for tubing, mounting taps, etc.