Love Tri Tip, and cook it every chance I get Yours looks great but I know what you talking about with the dry edges. I am thinking the secret is to cook it like a steak and not a roast. This works for me, and alway gives me an edge to edge rosy pink medium rare which will cure your complaint about dry on the outside. (that's the grey brown band at the outer edge of the cut you can see in the pics) . 1. I put my rub, (usually traditional Santa Maria, coarse kosher salt, cracked pepper, dried flaked garlic) on a least two hours prior to my cook. 2. Put it in a glass baking dish and cover the top with plastic wrap and put it in the fridge. Moisture will leave the meat and then be pulled back in along with the salt but you need the full 2 hours or even more if you have the time. if your Tri Tip is really fat on the thick end, you can even set a bag of frozen peas on top of the thinner end to make it colder. 3. Don't bring it up to room temp, but put it on a hot grill straight out of the fridge. Sear it first and then bring it up to 125 IT slowly, Pull it and put it in a cooler for 30 min. Perfect every time edge to edge. Just my two cents