Yes water is something you want to keep away from methanol. If you have a 44 gallon drum, keep it sealed at all times. Methanol turns to jelly when its stuffed and goes off. The last thing you want to be doing is putting jellified methanol thru your fuel system on your car. It will clog up everything.
In regards to the rubber, it will be ok providing there is constant flow of fuel and the car gets used. As soon as you dont drive the car for weeks, the methanol will turn to jelly and it will make the rubber go all powdery.
If you dont use the car for weeks, i suggest running the car until it runs out of fuel with the fuel pumps turned off, then blow out the fuel line system to clear everything out.
My only other thing about methanol, you cant do short cold starts all the time otherwise the oil goes milky. Always get it to running temperature before turning the car off. Dont just start it, move it 10 meters and then turn it off. It fills the sump up methanol making it go milky. Makes it appear like it has a blown head gasket when it hasnt. Thats just the way methanol is unfortunately.
Ive played with methanol engines plenty of times before in my speedway career. Its very good but very costly to run.