@captainBOB, it is possible, i built it, although as a hint, i do believe the pieces don't have to be exactly in the right position for the car to pass, minor gaps are fine, but this is untested.....
i did a ALL Ground, in the middle of my 84th wave, this what i did, just maze with flamethrowers, cannon and heavy cannon, this could probably get you to over wave 100, make good use of the walls