I was thinking of doing a removable mount on top of my fiberglass bed cover. Is this a bad idea?

 

By installing the antenna on the cover.... a foot or more of the antenna will be below the roof line and will probably affect your received and transmitted signal along with the SWR. If you decide to install the antenna on the cover you will want to install a sheet of metal underneath the fiberglass bed cover and attach grounding straps to the frame rails.... to ensure you get a good ground plane.....

OR 4x4