The interior seems to be metal.

I wouldn't worry about it breaking from lack of use since I use it, on
average, three days at a time two or three times a year.

But given all the trouble it'd be to chain it open when I'm not using
it, and worrying about how dirty it'd get being outside, plus the
labor involved in hauling it outside, I think I'll just leave it in
the basement. The only reasons I thought about moving it were the
extra heat it adds to the basement when it's on (it's in a small, semi-
enclosed space) and the work involved in carrying beverages outside
and letting them sit in a cooler, vs. being able to keep them in the
fridge until someone wants one.

Thanks, everybody.