I can't speak from too much AM experience, but I can share my
observations from HF SSB, and, legal issues aside, it is my opinion
that 5 to 35 is worth the price of a few fast food meals. As JS
suggested, there are far worse things going on than QRO on 11 meters.

I usually operate at 20m or 40m at 10W, and when I can't get through to
a station I'm reading at R4-R5, boosting up to 50W almost always does
the trick. Going from 5 to 35 is a comparable dB gain, and I think it'd
be worth it.

My rig is capable of 100W, but I've only keyed up once at full power,
and that was to verify that it actually worked.

I'd suspect the antenna is a big part of the problem. Maybe it's not
tuned or grounded properly? As far as I know, there isn't any reason to
favor one side of the vehicle for antenna location. On the driver side,
you've got drive-in windows to worry about. On the passenger side,
you've got branches. For truckers, neither is really a big concern. If
there is any difference in radiation, I would bet a single antenna on
either side would have the same coverage ten miles down the road.

If you want to run phased twins, the distance between them is
important, as it affects the gain and radiation pattern, but there's no
critical distance that will give you the best performance. The closer
they are, the more like a single antenna they will behave. When you
mess with the phase angle between the antennas for different patterns,
the distance becomes more critical, but it's my understanding that
truckers are concerned with what's on the road ahead and behind.