Ray,
I have this very mount on my rig. I like it, but I had some grounding problems. Make sure you use a Dremel or small tool to clear some of that paint on the underside of the hatch. The mount attaches by using 4 small allen head set screws.
You can kind of see it on my CB install that I posted @
http://www.sccxterra.com/smf/index.php/topic,1498.0.html (SEE PAGE 2)
It seems strong enough, but I may add a spring to the base to assist in tree Branch deflection since 4' is a little tall from my mount spot. Your antenna should be okay.
I can swing down to the HRO in Kearney Mesa and grab one for you if you want to meet up this week? They were the cheapest I found for that mount. I'm off THU/FRI/SAT. Just PM Me
Lava (Thats kinda Catchy isn't it?)