This subject has surely been raised before! I used to change my standard lpg plugs every 10,000klms as the old saying was just change them anyways for the odd $30 they cost which is realistically correct.... i know the Platinums etc get 100,000klms but i have read even 'stock' plugs under normal driving conditons can last much longer than 10,000 and even more so for gas.....Is this true and are there any 'proper' ways to check them under full range and load? I have seen old Champion Plug Testers.....Just checking for a good spark while turning over is'nt enough......Does anyone have any factual/experienced figures on change intervals???

I assume you are using the correct spark plugs & the correct gap. If I remember, the replacement intervals were either 20k or 30k for lpgas plugs. Do you use a top end lubing facility, like Morey's or similar?
They make they engines last longer, lubes the valve guides & rings.
And use a LPgas compatable engine oil as well. Its usually thicker than normal recommended oil. eg: AU on petrol only 5/10w30 & AU on gas/petrol 15w40. as per Ford specs.