We made a Cajun Microwave out of a stainless steal ice cream freezer with foam and didn't worry about it. We fired it up as hot as we could get it and let it burn, that burned off anything that would burn during a normal cook. We fired it up a second time and ran it normal to check if anything else will burn. It's been working great since.
I would run it at 325 for a while to check, if you smell it burning then keep the fire at 325 till the smell goes away and you're all set.