I think it unrealistic to contemplate fulltiming by moving the trailer around from place to place hoping to park for free, especially since you're tied to a job location. Please don't take this step unless you have a tenable long term plan for more regular places to park the trailer.
Per occasional overnighting in "non-campgrounds":
I rarely pay to overnight when I'm on the road, but when staying in "undesignated short term campgrounds" like rest stops/Walmart/private lots/roadside I abide by two rules:
1) ALWAYS know the local rules: that means ask permission on private property and check local regs governing public property.
and
2) NEVER unhitch the trailer. I think it prudent to be prepared at all such times to move at a moment's notice if necessary.
