If the body panels on your pickup are are double sided then installation will be more difficult as you may have to cut an access hole to install the mount, the roof might be your best bet as they are usually single sided and just require removing the head liner but roof mounting a 102'' whip creates height restriction issues.
Don't quote me on the bed being double sided but an easy way to check for this is to gently tap on the side with your opposite hand on the inner side and if this is the case then it will most likely be your easiest mounting location.
Good luck with your install.