If you are going to continue using the chest freezer I would recommend coating it with some epoxy paint after neutralising the rust. e.g. KillRust
Now, I don't know if it is an issue, and I hope others can clarify, but things like Tetanus thrive in rust.
Right. I have some rustoleum primer and paint all ready for when I empty this thing out next week. I have another chest freezer that I've already painted. This one's next. Unlike refrigerators, there's no moving air / drip tray in a converted freezer. So, if you don't use a dehumidifier, the humidity stays high. I do have a little humidifier for it actually, but I rarely use it.
Every month or two I bleach it. That's probably one of the reasons it's falling apart so quickly. So, regardless of how it looks, it probably doesn't have much fauna that I didn't put there myself
Saccharomyces, PC, PR, maybe a bit of lactobacillus.
BTW, I spray the sausages with Penicillium Candidum to keep the other worse molds at bay.