Guys, keep in mind when you call companies like USAA ( I also am a member , but I insure through American Family ) , Geico, Progressive, etc. and they tell you they do not cover something, it could be State specific. Before we start telling folks they are wrong about coverages or ability to acquire please remember what is available in your State could be completely different elsewhere. I have seen some huge differences, over the years, selling vehicles in almost every State in the Union, and the variances can be strange and confusing. Again, check with your Agent, and note that what one can get in Texas, may be completely different for coverage in Maine, or California, etc.
Honey Badger I would check with your carrier on Stated Coverage or look into Hagerty, Grundy, K&K, etc. who do specialized insurance for track cars and trailers.