Rear Roll Pan Installation

[rcg66]

I have a 66 Longbed Fleetside and need some help on installing the rear roll pan. Do I need to take off the tailgate before installing it? If I remove it, how do I bolt it back on after installing the roll pan? I don't think I will be able to get at the bottom bolts for the trunions with the roll pan on. If I leave the tailgate on, I don't think I can get to the top edge of the roll pan to attach it. Seems like every time I think something is going to be easy, a roadblock appears. Thanks for any help anyone can give me.