A little off topic since probably none of the 12v freezers have autodefrost.
Re "freeze burns" as techguy noted. Our neighbor served great peach pie from peaches they grew. When asked she said the peaches were from a good season 5 or 6 yrs. ago. I was shocked & commented such; she said the key was manual defrost[& she made sure there was enough juice to cover the peaches]. They tasted fresh. Re defrosting she said 1x/yr tops; my experience has been 2 to 3 yrs. with getting into the freezer 6-10x/mo.