Was your rig protected from the wind? Wind is usually the worst culprit for temp control. Cold ambient temps or continuous precipitation won't have much effect on temp swings...either the fire box will put out enough BTUs to get you where you want to be, or it won't.
Also, is your wood completely seasoned (dried)?
The thing with solid fuel fired smokers is that a constant temp is nearly impossible, especially with smaller rigs (with the exception of using the minion method with charcoal). As the fuel supply burns down in volume it will put out less BTUs, and as more fuel is added and it begins burning the BTU output will increase. Temp swings are normal and expected.
I don't have a stick burner, but in my charcaol smokers I try to maintain an average temp somewhere close to the desired chamber temp. If it peaks at 25* over after adding fuel, and then drops 25* below before adding fuel again, I just keep a mental note of it.
With a side fire box, you can reduce your peaks and valleys in chamber temp by adding fuel in smaller amounts more often. It's more fire tending, but if that's what it takes...
Probably not the answer you wanted to see, but some insight and food for thought if nothing else.
Eric