If fuel or gas escape into your boat from your portable engine or generator
there could be a serious risk of a fire or explosion. To reduce this risk all
portable LPG/petrol internal combustion engines/generators with integral fuel
tanks must be stored in accordance with the requirements of Standards 7.2
through to 7.8 when they are not in use, e.g. in a fire-resistant drained locker.
This will help ensure that any escaping fuel or fuel vapours drain overboard,
rather than into the boat.

It's also a good idea for you to store portable diesel engines or generators
securely when you're are not using them. [5.8]

When the portable tank is disconnected from the engine, it must either be stored in a fire-resistant container, stored on open deck where leakage can go straight overboard, vented near the bottom and piped overboard (similar to a steel gas compartment) or removed from the boat completely. The same applies to petrol generators when they are disconnected from the electrical installation. You just can't take risks with petrol when an appliance is not in use. [5.8]