This. Skip the extra insulation and keep the freezer full. This is no different than a house condenser sitting in the afternoon sun in 100+ degrees trying cool a house… freezer may be a little more sensitive though. Small box fan may aide in air movement. I’d be more concerned about the amp rating/wire size of the circuit, how many other units are on it, GFCI protected, and how often the units are monitored for tripped breakers…No insulation around it and yes it'll cool fine. The fuller the better. We did it for six months from about April to September when we were moving between houses in Texas and heat was in the hundreds. Storage units aren't air tight. They vent just fine.