Making a base for my station
Sonotube (The easy way)
Dig a hole about 20" deep and insert an 18" length of 12" diameter Sonotube. Make sure it's level. Place a piece of PVC pipe in the centre of the Sonotube and have someone hold it in place while you pour the concrete. Chances are it won't be in the centre of the base when you're done. The pipe needs to be big enough for your tower and should extend 8 to 12 inches above the concrete base. Double check the level of the PVC pipe before the concrete begins to set, if it isn't vertical you'll be digging the whole mess up!
Replace the sod around the base and water the heck out of it for a week or so. Place the wind tower in the PVC pipe and drill a 1/4" hole through the PVC and the wind tower pipe. A nut and bolt through the hole will lock the tower in place, if it should rotate your wind direction would be wrong. If you have a cabled weather station it's a good idea to place a piece of conduit in the base before you pour, then you won't have the cable coming up the outside edge of the base like I do. I recommend this in order to avoid cutting the cable or damaging it with a mower or grass whip.
The completed tower. Note the solar panel on the Integrated Sensor Suite, it runs the daytime fan aspirated radiation shield.