In a small bowl combine the salt, pepper, thyme, garlic, fennel and crushed red pepper. Mix to combine and set aside.
Remove the giblets and neck from the chicken. Use paper towels to pat the chicken dry on the inside and outside. Sprinkle a teaspoon of seasoning mix inside the chicken cavity. Fill the chicken cavity with the onion, garlic and fresh thyme.
TRUSS THE CHICKEN:
Cut a piece of kitchen twine about 30" long. Tuck the ends of the wings back behind the chicken (like you were putting your hands behind your neck) until they stay put.
Bring the string under the tail of the chicken and over the drumsticks, drawing them together and tying tightly (but not in a knot). Hook the string under the tip of the breast bone and pull the string up along the sides of the breast bone between the legs and the body, along the breast toward the neck.
Turn the chicken over so the bback side is up and draw the string over the elbow joints of the wings to the back of the chicken. Pull the string snugly and tie in a knot. Tuck any hanging neck skin under the string to hold it in place.
Let the chicken rest for at least 30 minutes or up to several hours or overnight with the rub before cooking.
SETTING UP THE ROTISSERIE:
Set up your rotisserie according to the manufacturers instructions. For a GAS GRILL, remove the grill grates and set a drip pan above the burners to catch any drippings.
Heat the grill to 425°-450°.
Slide one spit fork onto the rotisserie shaft and tighten. Thread the chicken onto the spit and secure it in the center of the tines of the spit fork. Ensure that the chicken is securely held. Slide the second spit fork onto the rotissierie shaft and secure the bottom end of the chicken with the tines.
Arrange the shaft on the rotisserie mechanism according to manufacturers instructions. Start the rotisserie and cook for 45 minutes. Use an instant read thermometer to gauge the doneness. You want to cook the chicken until it reads 180°F in the thickest part of the chicken - usually the thigh (without touching bone). Make any adjustments to heat or drip pan and continue to cook the rotisserie for an additional 15-20 minutes or until you reach the desired temperature.
Use grill mitts to remove the rotisserie from the grill and transfer to a cutting board.
Remove the spit forks and shaft and let the chicken cool for 10-15 minutes before carving.