I didn't use the Permatex on the bottom. I put a continuous bead up one side, around to top arc and down the other side. The door sits tight on the floor. I suppose you could try it. My door requires the top be tilted toward the dome to fit under the outer arch. I would probably be scraping a bottom...

Ooh, I like the idea of using the Permatex as a way to ensure a good fit. And I have enough left in the tube to do that, which seems like a great use for it.

From browsing around online it looks like vermiculite board might abrade relatively easily, but otherwise its properties look promising....

I'm working on a new insulated insert to fit behind my door. Going through some of the same decision points that you are. I use the insert plus the door to retain heat when not actively cooking. Otherwise, I'm just using the handled door. I'm experimenting with materials to decrease heat loss around...