Accessing the bed between the plastic & body (fender liner or bed rail cap?)

I'm working on bolting some Quick Fists to the inside of my bed to mount a shovel. Any suggestions for getting between the sheet metal of the body & the plastic of the bed nearish the wheel well? Trying to figure out how to avoid creating a 4 foot long wrench to put a nut on the back of the bolt holding the Quick Fist

I was going to pull the liner in the wheel well, but it looks like it's rivited to the fender flairs. Any suggestions on how to easily remove it?

Or is it relatively easy to pull the top cap plastic piece on the sides of the bed?

 

Yank the cubbies above the wheelwells.