I got some good suggestions for a mobile amp, thanks to all who answered
in honest help.

The next puzzle piece is a wide-band mobile antenna. I'm primarily
interested in operating in the freeband region. Coverage of the upper end
of the 11m band would be desirable too. I don't want a giant 9 foot whip
screwed to the bumper or one of those mobile monsters that have a loading
coil made out of coiled copper water pipe stuck on the roof either. I was
thinking about something along the lines of a 4 foot firestick. I would
assume it would handle the 500 watt amp OK. What about two antennas, each
one tuned to cover a part of the range with some overlap, and a coax
switch under the dash to switch between them if one won't work? Anybody
use a setup like this?

MeatSack...---...
Skywarn-NTS