While I agree with Wiz's definition of "boondocking", I think we all knew what the OP was talking about, and there's nothing to be gained by hassling him over it.
To me, there's an attraction to the OP's idea that distiguishes it from stopping overnight in a Walmart parking lot (which I continue to laugh at). For many people, a health club or gym is a destination in itself. Not only that, but their prepaid membership entitles them to UNLIMITED use of the gym facilities. Even better, 24 hour would be overjoyed if members grew so obsessed with the product that they camped out in front of the location and made vigorous use of the facilites in the wee hours of the morning. These gym memberships thrive on obsessive behavior.
So when I picture the possibility of all those active people camped close to what they love and getting the most out of life, and then I drive into my local walmart and have to navigate a maze of rotting heaps and decrepit lawn furniture, and then I read here how paying customers ought to be more considerate of those obnoxious, angry people sleeping in the parking lot, I grow convinced that either I or the rest of the world have it completely backwards.
Hope this helps!