Preventing stratification in the keezer and cooling a tower are two separate needs, ime. For the former I have a 120mm pc fan perched on the hump blowing across the length of the cabinet, and for the latter I have this:
The 1" ID PVC tube is stuffed up the tower column ending in the middle of the t-box while the fan dangles down roughly in the middle of the cabinet. There's enough room inside the 3"d column for air to return from the faucet box, and the 40mm fan moves enough air to keep the tower within 10°F of the cabinet even in mid-summer...