This is one area where I don't play it completely safe because I haven't found a good answer.
I kept a green 5l plastic petrol can on a shelf in the anchor locker and moved it to the sugar scoop when in use. Now I've changed to Camping Gaz there's enough space left to fit it into the gas locker. So that's one problem solved.
Unfortunately that leaves:
1) A 9 litre metal can in cockpit locker (fortunately very solid and filled with explosafe mesh)
2) Honda 2Eu generator in cockpit locker (thinking of building a sealed storage box)
3) Small O/B upright on bracket in lazarette (carb. always run dry but 1 litre in tank)
No sign of any leaks so far and never any smell of petrol when living on the boat for 6-7 months. All petrol used up or drained into plastic container (~1litre currently in gas locker).
I can probably improve matters with a box inside the locker and might be able to T in to the gas locker vent. However, I haven't come up with a plan for the Outboard yet. Pushpit is pretty full already and locker storage is much more secure (it's locked on a bracket out of sight). Still, any suggestions gratefully received.
my boat has an outboard in a well, the engine is stowed whenever sailing any distance.
Mine happens to be a nice light 2-stroke, but same applies; yes I do disconnect the external tank and run the carb dry whenever possible, but on the occasions I've been in a hurry and stowed without running dry I haven't found any leaks.
My Mariner 5 came with both internal and external tanks, I removed the internal one to save a fraction of weight but more to avoid leaks in the locker.
The main external tank lives in a dedicated locker - sealed from all others and vented - next to the well, I also carry 1 gallon cans which are wedged upright in another locker.
A very handy thing to have for top-ups if motoring far in calms is a splash proof funnel, it has a curled lip to prevent sloshing fuel around, and a handy guaze filter for those less than special marine fuel suppliers.