We have one -- they are a pain in the butt to clean. I had been using my method of Scrubbing Bubbles, a Magic Eraser, and taking a shower while scrubbing the thing with my feet, but I found a new solution. This was about 500% easier, and unexpected. Easy Off Fume Free oven cleaner. You spray that on, leave it overnight or 8 hours, then simply remove with a sponge or rag and a little water. It comes right off -- I only had a couple of places that needed any sort of real scrubbing to get loose. I did read online though you have to use the Fume Free because it has a different chemical composition than the other ones.
Here's an example:
https://youtu.be/lfMSlJp9qBE?t=21