the gas bottles are always only filled to about 2/3rds of what the vessell is capable of withholding so it will be fine, I have had these sitting in direct sun in 45 deg temps for days without trouble (take a look at the long term vans in caravan parks), if you can, place them in the shade if not, dont worry too much about them

the petrol in the generator may tend to weep out of the lid a bit if you keep it constantly full to the brim on hot days, best not to fill right up

diesel containers may develop a bulge if left in direct sunlight, if you see this then just release the cap a little and let the pressure out, same thing on freezing nights

usually these things can withstand enormous pressures and temperatures if handled in the abovementioned way, we have travelled in both extremes of temperature carrying fuel and gas without a problem

Thanks Guys, just what I needed to hear!
Cheers!