A cover and a gas shutoff is usually enough.

In areas that don’t freeze hard, you don’t need to drain the heater or blow out the lines. The real threats are corrosion from moisture and critters nesting inside.

Just turn off the gas valve (both at the unit and the main supply if you’re paranoid), then put a weatherproof cover over the heater. That’s it. If you have a heat pump, you might want to disconnect the electrical and cover the disconnect box too, but the pool heater itself doesn’t need full winterization.

I wouldn’t bother draining unless you’re in a zone that occasionally dips below 32°F for several days straight. Even then, just removing the drain plugs and letting water run out is enough—no need for an air compressor.

Your biggest enemy is a mouse making a home in the burner compartment. A cover solves that.

Don’t overthink it. Mild winters just mean store it dry and keep the pests out.