Always tie to an unsprung part (such as the A arms) rather than the winch/towbar/body as this will let the body move on the suspension. If you tie to the body you risk the body moving and snapping the straps.
Imagine the trailer going through a dip in the road, the trailer springs compress, the CF springs compress, the tie down straps go slack and when the trailer comes out of the dip all the pent up spring tension releases and gives a sudden snap to the straps, possibly overloading the tensile strength of the webbing material or the rachets, possibly losing your buggy.
Tying to the winch is also bad as it can overload the gear teeth (in road situation above) and bust them off destroying the winch and losing tension on the cable.
I have towed many different cars and bikes on trailers around Australia with it's less than smooth roads and have not lost one yet, but have helped pick up a couple that had been tied to the body and snapped chains.