Frost-free is not good for long term food storage. That's because the freezer automatically periodically warms up to over 32 degrees to melt the accumulated ice on the walls and floor. That water is drained off and the temperature then drops again.
Actually, I don't thinks it is anywhere near that bad. As I understand it, at least on modern frost free models, the coils are tucked away behind a panel, and a fan circulates the inside air over them. Only the coils get frost on them (they are the coldest part), and only the coils are heated (with the fan off, so the air around the food is not really heated much at all). The water drips off and through a tube to the drain pan (which evaporates with the hot air from the compressor blown over it.
They can actually apply quite a bit of heat to the coils directly to do it fast, and they sense when the temperature of the coils rises above 32F (which won't happen until the ice is melted). So it doesn't run the heat any longer than needed.
On our manual defrost freezer, the coils are in the shelves, and that is where the ice builds up (and grows from there).
Think about it, if they warmed the whole compartment above 32F, it would still take a long time for any frost to melt with all that food in there keeping the temperature stable. And the water would drip all over. Have you ever opened a frost-free and actually seen water dripping anywhere? Not me (unless it was broken).
The other thing - since that defrost cycle is removing water from the air every cycle, there isn't enough moisture to frost up on the walls. I think it is this dry air (freezer burn) that has more detrimental effect on long term storage than a slight temperature rise of 10 minutes once or twice a day (or whatever it is set for).
-ERD50