If it is a one lane road, and I'm towing, and the shoulder is safe, I might pull over and let people by (it is the law in Texas if three+ people are stacked up behind a slower vehicle anyway.)
If there are 2+ lanes, I don't worry. Austin has some pretty bad drivers -- During a local festival a few years back, there was a "hypermiling" group giving lectures of how to get 50-100+ MPG on a highway, especially in a hybrid car. One was drafting (i.e. tailgating), and the other was something called pulse and glide... i.e. accelerate to 70-75, coast until at 45-50 (the minimum speed limit) MPH, accelerate again, repeat. The problem with that advice is that the damage caused by a wreck or someone hitting the road rage limit is a lot more than the gas saved.
One recommendation I have: Buy a dash cam, preferably one in the front and back. That way, if someone does ram the back of your vehicle, you can hand the police a SD card with the video on it of them tailgating.