Hi Ken, while reading this post something jumped out at me. There's something that doesn't sound right about your gas tank filling procedure. You're not actually filling with a gas but with a liquid. Any "expansion" occurs immediately the first bit of liquid goes into the gas tank until pressure in both filling can and gas tank are equalised after that liquid goes by gravity into the gas tank. When the gas tank is full liquid will splutter from around the filler adapter nozzle. During filling there should be no "venting noises" only, if you listen carefully, the tolnk toink sound of liquid drops falling into the gas tank and the tink tink sound of gas in gas form going up into the gas filling can, just as you would if you were filling with water. When tank is full it shouldn't be very cold and should certainly not have "frost" on it. Cooling of the gas tank only occurs when gas is being used as the latent heat of evaporation needed to turn liquid to gas is sourced from the outer part of the gas tank. You may feel the filling can get slightly cool during emptying and to speed up the filling wrap your hands around it. I have a similar piece of kit and my gas tank takes about 45 to 60 seconds to fill. My launch is an open boat and I fill my tank in situ(against general advise) the small quantity of gas that leaks when tank is full and filler removed doesn't go pop on lighting the burner. If, as occational occurs, the burner goes out and fills the boat with gas I just tip it out and relight. No pops or singed hands and eyebrows! That does however occur if you tilt a full tank when lit (launching boat) and as a result the burner is supplied with liquid and you get a big yellow flame out of the flue. Scary but not a problem. Just turn off the gas. As to your leaking gas control valve, I can't speak cos I don't have one but I would find and stop that leak BEFORE I raised steam.
Best of luck, it's looking great.
Jerry.