Tim
I read a post somewhere on here about how to test that. What he did was deploy his TM while it was sitting on the trailer. He set the spot lock and had his wife pull forward in the truck and watched the TM. According to him the TM did not react until she got about 15 ft away. Then she backed up and it went about 15 ft past the original postion before it tried to correct. Sounds pretty ingenious to me. He concluded that 15 ft was about the best you could expect and seems to bear our the comments others have made about how close it would hold you.
In any event, soon as I get past Christmas and taxes I am getting one.
SeaRay