When my homemade tower cooler is off the freezer runs for 8 minutes then takes about 1.5hrs before it turns back on. I do have the collar lined with 2 layers of R8ish insulation and I beefed up the insulation in the tower
I have it about 3 or 4 inches away from the wall. When i need to get inside, i just pull it away from the wall to open the lid. I have the unit sitting on 4 large oval furniture sliders I bought at Lowes. It slides easily when I need access
Top is layed over a piece of 3/4" plywood with t-nuts. I then laminated over the plywood with black laminate so you cant see the plywood through the plexiglass. T-nuts are in the 4 corners of the lid and 4 through bolts through the tower assembly. Total of 8 bolts.
No air gap, I did leave 1/4" on each side to help get it in. The panels are only 1/4" thick mdf, I have the perf metal over the compressor and the back is wide open and away from the wall.