Bicycles. I have a 2x6 that I have mounted locks to hold the front forks of 2 bikes. I made a template that was width of the bed and 12" deep to simulate the front of the retractable cover. In order to make it work, the tailgate will have to be down with the rear bike tire sitting on it.
Seems if I do either the folding cover or the retractable cover, I'll need the cargo extender to keep things secure.
I can't see another way to carry the bikes in the bed. I could always get a hitch mounted carrier but I'd rather use the bed.

On the motorcycle front. I have a Goldwing and definitely wouldn't want to load that beast into the bed!