The real world and modeling are a lot different with vehicles than they
are with land mounted antennas. Your ground on your truck is very complex.

side question: Did you bond the bejabbers out of the truck? You
really should have hood, doors, tailgate, exhaust system in several
places, frame in several places, radiator, engine block, and any other
place of interest you can think of.

Rule of thumb is that you need at least one more bond than the maximum
amount you'd dare to place on the vehicle.

The vehicle bonding and grounding is more important than the aerial part
IMO.

- 73 de Mike N3LI -

The frame is the only substantial ground and certainly most effective for 40
meters. Use of the corners of the vehicle might actually get you a
counterpoise on 20. What you really need is a trailing wire, dragging a
cast iron stove.