This 3-way switch is actually rated 3A 250V or 6A 125V. It's called a "rotary switch." I just picked it up at my neighborhood hardware store for $5.95. I haven't weatherproofed it yet.

I had one just like it before, it never malfunctioned until one of the wire leads broke. After that, it became a 2-way switch. Maybe some Liquid Tape around where the wire leads attach would help keep water out.

Google a bit, you might find something mo-betta. For example, here's a waterproof cover for a toggle switch--

http://www.maplin.co.uk/module.aspx?...=2348&doy=10m6

A rotary switch works by twisting the metal cap clockwise, like on a table lamp.