Originally Posted by grumpus

Or just use blocks to space a bought fork mount off the truck bed to allow clearance for the axle end. Wood is strong in compression, the forces that would be placed on a block drilled to take an axle would tend to split the grain, although probably not a problem with a substantial lump of hardwood I would steer clear of softwoods. I made fork holders for roof bars using cheap QR axles complete with cones and locknuts, and square steel tube drilled to accept them, which was bolted to the roof bar. For a thru axle version I'd start with something like 12x15 mm hydraulic tube and some U bolts.