DaveR wrote:
What is the ideal tool to use to ensure that the fittings are properly
tightened, but not overtightened?

Frankly it's always bothered me when all the instructions say is, "do
not overtighten." That leaves it open to opinion. Your idea of
overtighten is not my idea of overtighten, and both are probably
completely different from the manufacturer's idea of overtighten.

Ideally, they'd provide a torque spec, but then you'd need to rent/
borrow/buy an expensive torque wrench, or rig up some Rube Goldberg
contraption with a scale to measure torque.

From a technical standpoint, you want the joint tightened to the
minimum torque where it doesn't leak: Use a standard wrench, and
gently increase the torque little by little until you don't get any
bubbles when you slather soapy water on the joint. Obviously, with
natural gas involved, this is not an ideal method because you could
well have the house full of gas before you get the joints all tighened
adequately, so you need to GUESS. Use your best judgement. Don't
noodle-arm the wrenches, but don't go HULK SMASH on them either.
Unless you're a total wimp or a massive body builder, your idea of
tight-but-not-too-tight will be close enough.