No post required, on some boats. We rigged a 23' cuddy 2 years ago by mounting a downrigger motor and it's spool and ran the line from the spool to a sheave ahead of the main spool. It is mounted on the hardtop post on each side of the boat. No more winding by hand, it sure is nifty.
A warning about using weed wacker line. It has a tendency to break down over time, maybe sunlight, and small burrs and kinks in the line will eventually stop the clips attached to your fishing line to easily slide down to the board.
dingbat, the small boards like the Church brand are far too small to use on choppy waters where we fish, Erie and Ontario, they will flip over. We use boards that are at least 5 lbs, almost 3 feet long and a foot wide.