It is legal but there is a maxum length, It used to be 58' but I think it is shorter now. Call DMV in Frankfort and they will give you the length and also get the persons name that you get it from just in case you do get pulled over.
I was going to green river and got pulled over in Liberty, I gave him the State Troopers name and he went to his car and made a call and came back and he said he was sorry and that I was legal.