Ed, K7AAT wrote:
"....but as I stated, most of my parking situations preclude putting out
anything beyond a short perimeter around my rig.... necessitating a
vertical, (with very short radials at best)."

Phil faced the same challenge. Item (1) of his summary says:
"Carry a complete set of mobile whips for lunch stops, or other
occasions where you do not have the time or room for anything better."

First on the list in Table 3 is:
"Hustler 75-meter mobile whip mounted vertically on the rear corner of
trailer...... S7"

Item (2) says:
"If at all possible, use a 1/4-wave counterpoise clipped tothe trailer
when using a mobile whip."

Second on the list in Table 3 is;
"Same as above, with 60-foot counterpoise wire connected to
trailer...................................S9"

So the counter poise adds about 12 dB to the signal.

A 15-ft high (at the center) 120-ft long dipole is S9+20 dB in Table 3,
but surprisingly the loop including the trailer is its equal. The loop
is only 30 feet long, or almost the length of the trailer.

Best regards, Richard Harrison, KB5WZi