I'd worry about tailgaters in traffic!
Something that I use for portable testing that does not involve connection with the bumper or trailer hitch...is sold in the lumber section of Menard's (an upper Midwest chain similar to Home Depot and Lowe's). Four pieces of 2" thick lumber with two cross pieces underneath that are attached with a nail gun. Measures about 22 x 22 inches, and have been on sale recently for $4.29. Add one or two 20 pound half-blocks of cement, and you have a very good portable rig for temporary gigs. Predrill some holes and insert carriage bolts through the bottom, that match your universal mount, spin appropriate machine nut or even wing nuts onto each bolt, thus allowing all parts to be packed in very compact form. I brought five of these to Atlanta and did not use them all....but fit all antennas into the back of a Ford Taurus station wagon.
Mike
