YES BED OFF!
I did all my tank & filler install with the bed off before I painted it and in my case even the fender off to do the last part of the fillers to make sure the over flow box would fit the angle of the fenders.
Remember the rear filler I had to make up from parts as flare sides did not have rear tanks.
I did have the need to drop the rear tank but got real lucky I could lower it to get the new sender out to swap a float that went bad and that was a bear!
I dont have a easy way to lift the flare side bed off as there is no bed rail lips to get anything to grab onto it.
The stake pockets are smooth on the inside so cant hook anything in them.
Guess I could grab on the vary outside of the rail but I then need to keep the hooks from sliding to the center and the big one not hurt the paint!
Dave ----