Neil,
I'm pretty unsophisticated, I'd just do a few trial jumps on the area to get a feel of how much 'oomph' it took to spring it back down. If you go a hair too far it would be easy to slowly jack it back up.
I just looked under my cab and there isn't much structure holding that panel. Maybe my approach is too crude for you, but that's the first thing I would do.
Stuart
