Just installing my new bed on the 40 and with the bed sides sitting on the cross members and wooden blocks and rubber shim the gap between the bed and apron is tight. When I lift the box to install the wood ( 3/4" thick) under the corner strips, the gap between the apron and bed is that 3/4". Running boards hang down approx 1/2" under cab. Should I shim the running boards to narrow the gap or strech the bed aprons to match. I'm about to mount my fenders and only want ot put one set of holes in the new bed sides, know what I mean?! Thanks in advance