Using a metal box on an extension cord is tricky. I *think* the code says to not bond the ground to the box. And then the receptacles should probably be orange as in isolated.
for storage and protection, a small steel shed works fine. Just put fixed louvered air grates in it. There's no need to have closing louvers.
A rain cap on any exhaust ducting advisable.
120V compared to where?
They need to read 240 compared to each other. Whether or not you have 240V at the service depends on whether or not the two hots are on the same side of the panel, or opposite sides of the panel, and that is determined by the style of breaker and how it plugs into the panel.
There should be a wattage max. rating decal near the socket.
my opener is rated for 100W X2. I put the clear ones (non frosted) they are a touch brighter.
There are special opener bulbs at the local hardware store (rough service) but for the cost of the clear 100watters at the dollar store I...