Michael, you don't say what year your Envoy is but looking at the specs for a 2005 Envoy XUV the towing capacity is only 6,000#s in the 2WD version with the Inline 6 cylinder and the GCWR (combined weight rating for both your Envoy and Monty together) is limited to only 11,000. (Your Monty weighs more than that by itself!)
You are severely overloading your TV (IMHO) and I fear risking disaster.
Bill