GMT800's have LATCH. I'd say from a liability standpoint, it is a BAD idea to try to retrofit LATCH into any vehicle. You have to follow the seat manufacturer's instructions for installation. I had no problems with numerous safety seats in my "older than LATCH" rides when my kids were younger. Many of them want you to pull the shoulder belt all the way out until it locks instead of auto-retracts, then tighten with weight on the seat or seat base.