pyscho - I don't use the belt tensioner on the top plate either, there's really no need for it. It's probably better to replace the belt then to use the tensioner.
I weighed my car with all the electronics plus a transponder and my car sat at 50 ounces. That's just as light as my FTTC3. With the body I'm just the legal limit of 53 ounces (without the transponder)