Doesn't this lead to the risk that your pay will drop as you face competition for the position with an increasing number of willing unskilled workers?

I'll have an experience edge over recent graduates by the time that happens. Besides which, the better working conditions would more than make up for it.

Worst case scenario is that I cross-train or cross-certify in truck maintenance, as "someone who can get the damn truck rolling again in an emergency" is going to get a much better paycheck than "someone who picks up the phone when the damn truck stops".

Actually, the real worst case scenario is that I lose my job and get out of trucking in general.