Don't do it in wood. But if you do, heed the warning about grain, and make them thick as possible. Like 4x4 PT kind of thick and dense. But just don't do them in wood.
Buy them, or just make them out of square tubing or a puck or block of something. You don't want these failing.
They should cradle it, and in best case, the depth of the slot should be the same as the height of the weld/flange, but no more. The flange is the strongest part, but cradling the metal WITH THE SAME depth is best. If the slot is deeper than your flange, it's a certainty you're going to pucker the unibody; the variable is how much, and not "if".
