The BMW Factory E36 Towing Manual specifies only one way to secure an E36 car to a flatbed truck or trailer -- by using something called a T-Hook. T-Hooks also work on all E36 and E46 chassis cars including M cars and Z3 roadsters and coupes.
Four T-hooks are inserted into a special access holes built into the E36 chassis and tie-down straps or chains fastened to the T-Hooks are used to secure the chassis to the flatbed or trailer. This is the best method for securing your car because:
~ suspension movement is limited, saving wear and tear on suspension components and providing a more stable load,
~ it is the only method approved by BMW, and
~ it is the quickest, cleanest, and easiest method by far!
Unfortunately, the manual offers no suggestions where consumers can even find one of these T-Hooks. There is no BMW part number and BMW doesn't sell them.
You may be able to buy t-hooks from a local towing supply company, but the easiest way is probably to purchase them online through Northern Tool & Equipment.
I no longer sell them due to decreased demand, but feel free to download my instructions for their proper use here.