questions for 4-hour serving event

So I just got this last minute request to cater an event for 80 people tomorrow. I'm just getting started and most of what I've done has been pre-order, pick it up when it's ready type stuff. For this one, they want 2 kinds of meat for sandwiches and I'll be doing a few cold sides. I'm not worried about keeping pulled pork warm and serving it over the course of 4 hours. What has me a little nervous is they want tri-tip as well. That's kind of a serve-when-ready meat in my mind. I'm worried that putting it in a chafing tray for 4 hours is gonna completely kill/over-cook it. The other issue is the budget they had for a taco truck is gonna make it tough to provide tri-tip anyway. Just wanted to see if anyone had suggestions for keeping medium to med-rear tri-tip in good serving condition for that long. Can it be done?

Thanks landarc. My dad and I were strategizing earlier today and came up with exactly the same plan, but I'm glad to hear you suggest the same things. Tri-tip doesn't really fit the budget for this one, but...it's a benefit fair my brother is putting on for one of his clients and the budget they had not only covers all my food costs, but the purchase of some equipment that I needed to take my show on the road (chafers, ice buckets, cutting boards, serving utensils, etc) and I'll still come out a little bit ahead. I figure for this one, if everyone likes the food, I end up with some equipment and a little bit of cash, it's a win.