I have two setups. On my Silverado dually (all steel wheels), I have braided extenders for the inside and they have yet to leak (good US-made ones). On all the wheels, I have straight metal stems. Works great. On my F550 chassied motorhome, it has 90-ish degree metal vale stems (Alcoa wheels on outside and factory steel on the inside). On the Alcoas, the stem's working end faces to the inside. Requires a double foot truck-style air chuck to fill and it works great as well. I'd recommend that style for your outter wheels (should be fine with steel and simulators if that is what you are running). The down side is if you need air, don't have your own compressor and the gas station only has the simple little round air chuck, you will be alying of the ground trying to fish your hand betwee the wheels to fill.
Double Foot/Truck Style Chuck:
