JRJohn,
To your knowledge, has there ever been an rc airplane related claim to an insurance company other than the AMA when the AMA was not the secondary carrier?

Wouldn't it be an uphill battle to convince and educate them about the law and rc airplanes and how that applies to coverage after the fact? As the secondary wouldn't the AMA handle that aspect of the case for you saving you possible legal fees in fighting your carrier for coverage. I may not be as experienced as you in insurance but I've had a lot of experience with high liability businesses and a company that specializes in a particular field will serve you much better.

I think it's a heck of a lot easier to just join the AMA and I don't believe they are looking to deny coverage.