Use THE "T HOOK", part number 50240-10, made by M&R Products, Div. of A.S.T.S., Inc. Vineland, NJ 08360. they are sold at trailer retail stores. The hook fits into car frame slots made for securing cars. The Viper slots(4) are located on each frame rail front and rear. The T Hook is 4" long, it has a T on one end that goes into the frame and a oval on the other end that accepts a tie down hook. Very easy to use and Nothing to Weld or bolt! I bought my T Hooks from Orlander Trailer in San Jose, CA. price $7.50 each, 4 required.
Tow rigs, at track events, should have a couple of these hooks for towing Wood Chucks.