I Use 4 x wide tyres (245 or 225's appear to be about right) and then 4x tie downs; tyres are the best becasuse they have a little give in them and so when you tie the boat down they give a little. Saw horses won't give; thus how ever tight you tie the boat down you will still get it bouncing around a little = bad.

The tyres give just enough to allow a little movement but still be very snugly tied down.