I have a few thoughts on different alignments but first I want to make a general statement. Mix it up. Do not stick with one defense the entire game. They will find and exploit the weakness. You might have a favorite that you use most of the game but switch it up to keep them guessing. OK, on to the ideas.
One idea would be to go man on their top guy. I don't think you could afford to go man on two of them unless you were all man. Against trips just take away the 1 middle linebacker in the 1-1-3. So you'd have man on their top guy, a rusher and three safeties that you'd shade over towards the trips side. That would place a lot of responsibility on the weakside safety because, he's the only one left over there. He absolutely cannot get beat so don't cheat him over too far.
Another plan is to design a zone specifically for trips. One rusher (always rush someone) and then stack a zone over the trips as follows. Two defenders stacked over the trips 3-5 yards off the los one on the outside shoulder of outside receiver, the other on the inside shoulder of the insider receiver. Behind them is a safety maybe 7-10 yards back right in the middle of the trips so it looks like a triangle. Your weakside safety will be all by himself again and needs to watch the center.
Modify the 1-1-3 so that the middle linebacker moves over the inside shoulder of the inside trips receiver. Weakside linebacker again has the whole side to himself. If you want to get fancy line up in a standard 1-1-3 and have your middle linebacker move right before or after the snap.
As I'm thinking through these plays I think I'd probably go 1-1-3 and see what they do. Maybe plan on switching to option 3 which is the most subtle change and see if that works. The other two are riskier especially if you sit in those too long. Most dangerous is the center position which would be an easy pass on most downs.
Good luck, let us know how it turns out.
Orange, thanks for the feedback! I agree, what I am thinking is starting in the 1-1-3 base defense like we have played all year and really depend on my rusher to put pressure on that QB. When they line up in Trips, I think we'll just slide the weak side safety over a bit and my front middle "1" a bit, like towards inside shoulder of inside WR, but have him ready to drop back 5-6 steps when its a pass waiting for the quick slant pass or clogging the middle of the field. Our guy is smart enough to do this. But he also has to watch sweeps going the other way, this is also where my rusher must play a vital role! My weak side safety has to watch the center running a post type of pattern to the weak side as well, BUT keep one eye on the middle of the field because that is generally where they like to attack ultimately. The bottom line is, I think we just need to play the way that got us this far and make any necessary adjustments along the way. This really comes down to my rusher and him getting massive pressure (which he is one of the best at) on their QB. This will lesson the amount of time the other defenders have to cover and give the potential for picks....