I always strap/chain vehicles by either the tyres/wheels of the suspension arms near the hubs. By doing this it allows the vehicle to move on its suspension as the trailer goes through bumps in the road. If you strap/chain the body it will slacken the straps/chains as your trailer goes over a bump compressing the suspension, then snap back as the suspension extends which I have seen break straps/chains. The other way is to snug your straps down so tight it compresses the suspension so much that it cannot compress any more (on the bump stops) but this will not do your springs much good.