Some of the links on this forum allow SMF, at no cost to you, to earn a small commission when you click through and make a purchase. Let me know if you have any questions about this.
For a commercial seasoning? One that is popular in my area is Pappy's Original. I prefer Pappys All Purpose, but either is pretty good on tri tip for a store bought solution.
I'm a huge fan of Santa Maria seasoning on TT. Santa Maria, CA is possibly the origin of grilled Tri Tip.
Store bought I'll use Scott's Food Products Santa Maria Style seasoning. For making my own here's my favorite recipe. It makes enough to last a while.
Santa Maria Tri Tip Rub #1
Whole Foods sells a Tri Tip rub we love but it is $6.99 for a small container (Scott's). I looked at the ingredients came up with a rub we can make ourselves that is just as good.
Ingredients
1/4 cup Kosher salt
1/4 cup finely ground black pepper
1/4 cup garlic powder
1/4 cup onion powder
1/4 cup baker's sugar
1/4 cup dried oregano
1 Tbs cayenne pepper
1 Tbs dry rosemary
1 1/2 tsp dry sage
For tri-tip I like using Tatonka Dust and bringing the IT to 130º and a 15 - 20 minute rest before slicing for medium rare. One big thing to pay attention to on tri-tips is making sure you slice it against the grain. Tri-tips are an odd cut of steak as the grain runs in different directions in 3 different area's in a Tri-tip. If you slice with the grain the steak will be less tender and more chewy. Here is a slicing diagram for a typical tri-tip.
Dry brine with kosher salt. Mince some live rosemary leaves and rub in. Then coat with some cracked black pepper. The beef has enough flavor and a herb and a spice brings it in to.. well.. awesomeness.
Last Tri Tips I did I used a Santa Maria seasoning from Oak Ridge BBQ. Very good stuff and excellent flavor. If I want something a little more bold I go with Quebec Beef Spice from the Spice House.