Tare weight and propane tanks

I bought a propane camp stove for the teardrop and since I'm keeping track of the weight of every last thing we're adding to our rig, I need to know the full weight of the propane tank. Bob already had a 20 gallon cylinder (If I understand it correctly, when full, that tank would weight upwards of 38 or so pounds?) There's no way I wanted to tote that darn thing on our camping adventures. Between the shoulder/wrist problems I have, and thinking we could save valuable weight space for something else---Bob bought me a Worthington 11 pound tare weight container (the shorter, squatter one, not the tall one). Trying to make sense of everyone's calculations on the net (all different), it should contain approx. 4.24 lbs of propane? Is that before, or after the space that's left for possible expansion in hot weather? I've seen figures of 15 to 17 pound full weight? Does this all sound about right?
Anyway, we haven't taken it to be filled yet----the service station a couple of miles down the road has a refilling station @ 1.19 pd. for propane.

Anyway, we haven't taken it to be filled yet----the service station a couple of miles down the road has a refilling station @ 1.19 pd. for propane.