What is the best way to cook baby back ribs on a propane grill?

There are a number of ways.

Season with salt and pepper or a dry rub. Try briefly searing all sides, then wrapping them in foil and baking in a 350°F oven for two or more hours. Place the foil wrapped ribs off center a hot charcoal fire. Leave them wrapped until the last 15 minutes. Leave dry at this point or coat with sause (I prefer Johnny Secreto Craft BBQ Sauce or Backyard Classic).