1) don’t fill up so full. No brainer
2) fuel today is not the same as fuel from when that system was designed.
You need to adapt. Like we all have.
3) gas hot water heater in a garage- make sure it is about 18-24” off the ground. How is that even code with fuel vapors hanging out at ground level.
You are very lucky! In New England we have basements for that stuff not garages. Even garages attached to houses are dangerous but legal. I’m lucky- our two car is a separate building. Only electricity in ours. Good thing your door was/ is open.