Well, a lot of it also depends on how solid the car is, structurally. If the rockers or floors are rusty or corroded at all, its going to be weaker and will need more support. Ideally, youd want something to brace it straight across the top of the door opening, since the lower the brace is, the more force will be exerted onto it, similar to the way a hand-held nutcracker works. If you drill holes in the end of your braces, or weld brackets to them, then you could just bolt them to areas of the car instead of welding them.
