I'd first see if the inner lining of the box can be removed and do so if able. Then clean everything left and replace the liner after cleaning it on both sides. If it isn't removable I'd clean the inside and remove the rubber gasket.

Next I'd sand the entire inside of the freezer and paint it with at least two coats of two part epoxy paint to seal it. Let it cure and then see if you wasted your time and money or sealed in all volatile components of the previous contents. If successful then replace the rubber door gasket. If not successful you have a compressor that will make a decent vacuum pump and a safe storage box for flammable stuff like paint, thinner, solvents and such.

Pat