Dieselnerd,
On my 04. 5 CTD, I have a Draw/Tite hitch installed for towing my 26' 5th wheel trailer. The kit frame sits on top of the frame secured by (4) 5/8" SAE hardened bolts ( 2 on each side) located on each side on the outer side of the frame kit flanges. Only two holes on the outside on both sides of the frame are drilled. Nuts on the inside of the outer frame are secured to the bolts. This is the HARD part. The weight of the hitch lies on top of the frame and not stressing on the bolts. This drilling is allowable. No welding at all neccessary.
The center of the trailer pin area sits 1 1/2" foreward of the center of the axle in mounting of this kit for best weight distribution on my truck. Not all fifth wheels are mounted centered directly over the center of the axles for best results. This is why slideing 5th. wheels are available. This installation is "fixed".
Line-X was sprayed into the bed before time. This is to the individuals choice. Either before or after is not important.
When the hitch is removed, 4 rubber "pucks" are pushed into the MT holes to keep dirt out. The bed is smooth with no obstruction. This is a neat installation. The four holes incorporate locking cams.
The Co. that installed this unit has been in business for 50 years now. They custom prefab. anything you want to specs. One last comment, if fender liners are installed, it is much easier to remove them for this work. I added the liners later. They really keep these trucks clean. Pull/Rite is a different Co.
Chuck