Question about gas fireplace?

I have two gas fireplaces, with metal tubes that run parallel to each other vertically. At the top, they are encased in a chimney chase. A foot from the top is a surrounding crown that surrounds the two tubes and is hollow on the inside. My question is this: Every year, wasps make nests in this hollow space (there is a two inch opening at the top and a one inch opening in the bottom). Is it safe to spray in Great Stuff foam (the high temperature one), on the inside of this hollow? I'm not sure how hot the tubes get at that height (maybe 200 degrees), and I cannot afford to have the chase replaced. Thank you for your advice