Many RVers take advantage of rest areas, especially to stop for a lunch break. Unfortunately, it is obvious that most RVers are not familiar with something that should be second nature to them—where and how to park.
RVers need to learn to park at the rear of their parking space, so that incoming truckers can see that the spot is filled before they start to pull into your spot. (The back of your RV or toad should be even with the rear demarcation lines).
Park away from the toilet area—let the truckers have the closer spaces. Most of them are only stopping for a pee break (and they won't be making lunch like a lot of RVers).
Park in the RV and truck spaces—not in the automobile spaces.
And, yes, sometimes there is "no room at the inn." Don't try to park on a shoulder and possibly block a trucker's exit path. Go down the road and find the next place to stop.
Remember that courtesy is a two-way street.