Caveat: The following works best on a Dodge truck but maybe rigged on other vehicles as well.
Sometimes the wind is blowing the wrong direction to cook on the tailgate. Sometimes my daughter has picked up stray kids and they're up & down the ladder & playing in the truck so it's nice to cook elsewhere.
Here's my new setup. Worked fine first time for me. Hopefully it may work for others.
Look ma, no leg camp table setup
Put plywood slab on 1x2s inserted into channels above rear wheel (either side of truck works. Use leeward side :-)
Shim 1x2s tight above tire. I'll be trying to improve this redneck setup but it works well.
Here's a final image of the 1x2s inserted into the channels.