Before my first visit to Fajitas To Go in McAllen, I was sitting with Joel Garcia at his joint, Teddy’s Barbecue, in Weslaco. I asked if he knew about the food trailer. He gave it high marks. His wife, Bernie, later told me, “That’s my favorite place.” After I posted a photo on Instagram of owners Jesus and Briana Martinez, the account for GW’s BBQ, in nearby San Juan, commented, “Those guys are awesome!” It seemed I had found the place where all the big Rio Grande Valley pitmasters eat.The smoke in the air from the grill was thick when I arrived at Fajitas To Go on a recent evening. The trailer sits in the parking lot of a bicycle shop and coffeehouse. Customers have…