The marinade we use is something many already have in the refrigerator or cabinet...low-fat or fat-free Italian Dressing. It adds a great flavor, and isn't expensive to buy. It's delicious on grilled thighs.
Take a large zip-lock food storage bag, and anywhere from the night before to a couple of hours before you're ready to grill, take your skinned thighs and put them in the bag, then pour some of the salad dressing/marinade in and seal, releasing as much air as possible before sealing.
For a family of 4, assuming each eats a couple of thighs, about 1/3 - 1/2 the bottle should do. Now lay the bag flat and move the meat about so it is flat and surrounded by the marinade.
You can turn the bag over 1/2 way through the marinating process, but it's not absolutely necessary as long as all sides of the meat are in the dressing.
You can store this in the refrigerator until you are ready to grill.
When it's time to grill, if you have chosen non-fat dressing, cook slower at a lower temperature than if you chose one with oils in the dressing.
Tip: Have a little dressing in a cup with a basting brush, and if your meat looks like it is drying out during grilling, baste it.