The worse you can do is start the engine and let it run for some time without riding for at least 30 min. If you don't want to go on the road for a period longer than 2 month, take the battery out and charge it once or twice.
But the best wy to keep your classic car in good condition is to drive on the road, and in a period of one or two month there is always a possibility on a dry surface.
My 1948 Dodge starts very well after two month without charging the battery, so I don't understand the 'problem"
I use a float charger only for my Harley because the bike has a very small battery and the alarmsystem can't be shut off; it works good.
For my Dodge and other classic cars I never need a charger