you have added fiberglass front fenders, they probably have a flare to
them making them stick out wider then the bedsides. The best way
to widen the bedsides to match the front without having to buy
fiberglass bedsides is to flare the bedside.
flare the bedside you start out by cutting the section of sheetmetal
up in the wheelwell that attaches the inner bed wall to the outer
bedside. Be careful - there isn't much room between the section
of sheetmetal and the wheelwell. You could cut right through it
leaving a visible cut in the wheelwell from inside the bed.
need to remove the supports in front of and behind the wheelwell
opening. You need to make new ones to bolt in place to hold the
bedsides out. These can be made from conduit or flat stock.
a homemade spreader like the one shown below, spread the bedside out
and leave the spreader in place. You need to attach a plate to
join the gap you created when you cut the bed and secure it in
place. It's best to weld it in. Be careful, if you don't
use strong materials the bedside will try to return to it's original
width and crush the plate.
spreader can be made out of a section of threaded rod, a nut to fit
the rod, a washer, a piece of pipe to slide over the rod and some
sturdy flat stock. Weld a piece of flat stock to one end of the
pipe and a piece to one end of the threaded rod. Run the nut up
the rod, slip the washer on and then the tube piece. When you
loosen up the nut, it should push the pipe down the rod. The
flat stock will push on the bed walls to flare the bedsides.
Make sure you make the flat section long enough to spread the load.