I had a pickup truck previously and made a mount for the forks that fit into the bed out of 2x8's and mounted 3 fork mount brackets (from yakima) onto them. I also used it for my trainer with minimum modification.

Our team rides on trainers for practice 5 times a week and we very rarely have to pump up our tires (front). I think that if you were losing that much air... you might have had a slow leak somewhere?

I guess... it depends on how often you're riding too though?

But yeah, I would just make a fork mount or use a sturdy structure or something.