I find it difficult to believe that non-maintenance free batteries can go for extended periods of time (e.g., more than a month or so) without needing water. But, that's just me!
The turkey baster works best for me. All of the other methods that I've seen are too clumsy or ridiculously over priced. Most plastic items won't last, including the baster. But, for a buck or two I can replace it several times a year and not get ripped off.
And, when home and plugged in to shore power for extended periods, I use a device similar to this one to keep house and chassis batteries charged.
http://www.batterymart.com/graphics/...ACC-1206WB.jpg
Battery Defender Pro 12 Volt 3 Amp
(Actually, I just noticed that the "Battery MINDer" is one of the advertisers here. Just so happens that that's the one I use. But, clicking on the link goes no where!)