I have felt the same way, my husband and I did a bunch of riding in British Columbia near Squamish last summer. While the roads were not very heavily used, they were used by heavy trucks (logging trucks, and the occaisional hay truck). I had been riding oh, 4 months or so at the time. Needless to say as the loggers rolled by (some closer than others), it always freaked me out that I could look to my right and see nothing but truck wheel. I just held my line and kept pedaling when they'd go by.
I think taking whatever road you need is the best option. Trucks and cars have to share, even if they don't want to. But I know that is easier said than done.
The good thing, is once I was back in Mass riding the backroads, cars seemed more my equal. But we still hear too often of riders lost due to inattentive or drunk drivers.

But don't give up; enjoy each ride you get to go out on, and enjoy each safe return a little more...