Way too much worry. There is low pressure. Just tighten tight, it's an interference fit. Put a brass nipple into the tank, then put on the valve and let it sit over night with a pan under it to leak test all those joints. No leak? Continue. Leak? determine where and tighten a bit. Leak test again. The most critical part is the gas tank female. If you bust that off, it's a bad day. You can use a paste type sealant for gas if you want to. Just don't have it near the starting end of threads. A little space of dry threads first. That way it won't migrate into the system.
If you have other places that you fear a leak, use a valve to temporarily close off to test. Of course you need gas in the tank for these tests. Don't use any long wrenches and keep your hand near the fitting, not on the end of the wrench, at first. Tighten real tight from there. Then slide out to end for a small snug turn. Never jerk any fastener when tightening. This is a no no in the engineering world. You have no idea or feel of the pressure at that point.
For small size threads, with your hand close to the fastener you can't over tighten and your natural instincts will tell your brain when to stop....or You can do what I do, turn til my elbow clicks.
If you tighten it real tight and it still leaks, you will have to take it loose and retighten it or get another Chinese fitting out of the same bin. The law of probabilities says the next one will work. Six Sigma. If it still leaks, park it over some weeds you want to die.
