Best fuse to attach a relay that will be switched by the ignition

Hi chaps I’m looking to attach a relay to my LPG system as it is drawing 50 mA while the car is switched off ( 74mA in total ) I’ve had this car for about a year and I’ve had nothing but problems with flat batteries I’ve change the battery and the alternator I’ve been through all the fuses in the car looking for drain when the car has shutdown. if I don’t use the car for for five days The battery is drained enough that the car won’t start so I’ve narrowed it down to the LPG system and want to switch it through a relay which will turn on the management system when the key has been turned so the question is where is the best positive attachment point or fuse to switch the relay when the ignition is switched on
Many thanks in advance

Fuse 5 20A on the front fuseboard isn't used and is ignition controlled. Should do what you want.

There are also ignition controlled sources in the black e box under the bonnet which would also work.
I did a description of these some time ago but I'm blowed if I can find it.

That’s excellent advice .. many thanks for posting