Hi Nat,
Nice little tank! Spraying it is a good idea. A dark colour is great as it adds depth when viewed from the front. I'd personally go for black like yourself, or a midnight blue, just to give it an ocean feel to it. Tape newspaper onto the sides and top to prevent any paint getting anywhere it shouldn't.
Probably the best way to do it would be to move the stand outside or into the garage with the door open and place the tank on it. That way you don't have to lay it on its front and run the risk of scratching it. Remember to do the spraying in a well ventillated area and you should really wear a 3M mask too.
The cold weather is also against you, due to the moisture in the air, so make sure to remove any condensation from the glass with a paper towel and ensure the glass is free from greasy fingerprints and dirt. Give the can a good shake for about 2 minutes before you start. Hold the can about 18" from the surface and move your arm in a slow sweeping motion, making it from left to right in about 3-4 seconds. Press the nozzle down with each pass and then release. Don't hold the spray in one location, just allow the paint to build up gradually and evenly. Keep a paper towel to hand too, as the nozzle can clog. Inspect it after about 4 passes and wipe any excess away. Doing it this way will help safeguard against the aerosol spitting and also against runs.
Once you've coated it, leave it for 30 minutes, then apply another coat, to make sure you haven't missed any tiny spots. If you can pick up a can of matt lacquer, even better, as you can protect the paint once its dry. Don't be tempted to move the tank until the lacquer has fully dried. Due to the snow and cold temperatures, the air is very damp and so drying times will be extended. If you take your time, the end result will be a perfectly painted background
