TGPR doesn't have walls.
Three cars on the track at a time is very safe. Even when Byron and Insite are running at the same time.
You probably already know you would have to talk to your insurance company regarding their position or offerings for tracking, and since this is not timed and there are other elements that separate it from being a race, the conversation would be similar to an AX situation.
This link has an aerial photo.
TGPR