A copper pipe, probably 3/4 will fit inside bed tube. You can by 2 ft at Home Depot for $8. Use 1 Ft each side. Mount bulb inside of copper as deep as feasible. Use round wood/plastic/dowel supports which are sized very close to ID of bed tube. You may want to cut notches in at least the rear support for two reasons: To slide in easier and air flow. The copper "heat sink" must be sized to leave air space between itself and ID of bed tube. 3/4 should work for leaving that space and for mounting bulb inside. The air flow and the fact that copper conducts heat 10 times better than steel, will keep the whole area cool by carrying away the heat and radiating it down the bed roll thru the air. There will be some heat "transfer" into the bed metal also. See my sketch. One sheet metal screw thru bed tube and into copper will hold it. Bulb flange touches copper. copper touches screw, screw touches bed= the ground. Maybe bulb flange can be soldered to copper to hold it. Slide all out for service. Wires routed out the back of copper towards cab. Pic on request.


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