Search:

JRB bridge should work well for you.

I was thinking the same thing. How wide is the double bottom? I'd think it would need to accept at least a 24" pad.

Welcome to the site. A Hennessy should work as a bivy with your motorcycle and a tree. I've never used it as a bivy though. What kind of pad do you have?
As to the JRB bridge, which I own, what is...