IMHO, NO it isn't necessary, you are buying PRIME cut beef, you really want to taste the delicious unaltered beef flavor, rub can help but not over power, but a marinade will mask that flavor.
This past weekend I did 5 Tri-tip on the grill. The cookout was at my Sis house for a Easter/Birthday/Daughter coming home party. Cooking on their new outdoor kitchen stainless grill. My sis provided the Tri Tips and her son marinaded them 24 hours in his favorite marinade which was a light Teriyaki marinade. His fiance father I met for the first time at the party, he is a huge foodie, a degree in Food Science and works in the food industry, and works with large commercial / industrial food production and processing companies developing food products or enhancing food products. He agreed that I cooked the tri tips too perfection, the meat was cooked med rare, was very tender and juice and lots of flavor, but it wasn't that big beef favor, it was a muddled something else flavor. In other words the marinade hurt the flavor not enhance.
Understand the santa maria style and cooking of tri tip is what put this cut on the map. It is hard to beat these prep and cooking method.How to prepare the most flavor tri tipAnother exampleEdited by deltadude - 4/5/10 at 11:54am