RE: Filtering Glow Fuel.
Water and petrol don't mix so they can be separated out via mechanical separation or filters. A quick check on the Mr Funnel website reveals that water in shaken fuel mixes can pass through the filters, letting the fuel/water mix settle allows the water to form big enough blobs to get trapped in the filter.
Water and alchohol mix completely and can't be separated mechanically otherwise teenagers would have figured out the they can pour their bottle of vodka through a filter and get 95% alchohol or better. Once the water gets into an alcohol fuel, it's pretty much game over unless you've got access to specialised equipment. I never put ethanol based fuels in my vehicles and have yet to experience this poor running after a few weeks but I have heard of it happening.
The stable temperature things is about preventing a partiailly sealed container sucking in and pushing out air every day, and as has been pointed out a properly sealed jug will puff up when hot and suck in it's sides when cold. The contents themselves don't really care about a 20 degree thermal cycling every day, although exposure to light is something that should be minimised
I filter the fuel going into the plane's tank, then from the tank to the carb. I figure twice is enough on medium to large sized motors although on some of the smaller engines people can be really fussy about it as their fuel passages are really tiny.
Like everything, people have their tried and tested ways that work for them and about the only wrong thing you can do with fuel is leave the lid open for a few hours in humid weather or filter it through a wet muslin cheese cloth.
Cheers