That's a great cooker. You're a lucky man.
I favor cooking butts at a slightly higher temperature than 225, and certainly wouldn't go below 215 for any length of time. In fact, there's not much benefit to cooking butt, picnic or shoulder below a target temp of 250 and the time penalties are enormous. Given the tight nature of a Stumps, you don't run much risk of drying the pork out anyway.
I favor an injection of apple juice and white grape juice mixed 50/50 or Liebfraumilch, Gewurz traminer, or a Johannesburg Riesling. That is, a wine that combines floral, sweet and spicy qualities. A little onion powder would not be amiss. Pork and onion are wonderful compliments.
You might find the following rub interesting:
8 tbs brown sugar
3 tbs (mild) paprika
3 tbs Morton kosher salt
2 tbs fresh cracked black pepper
1 tbs ground ginger
2 tsp granulated garlic
2 tsp granulated onion
2 tsp five spice powder.
You can kick this up nicely by toasting 4 tbs of fennel seeds and 2 tbs of coriander seeds, grinding them and adding the powder to the rub. Without the addition the rub is pretty straightforward, the fennel/coriander raises the whole project to a pretty sophisticated level. Definitely not for competitive barbecuing.
If you're going to use my sauce (see below), slather with 50/50 dijon mustard/mayo. Otherwise slather with plain yellow mustard or mayonnaise, and rub generously.
Prep the smoker to run at 250. Most woods work well with pork. I find oak, peach, hickory, apple, citrus, pecan or cherry work best -- singly or in blends. If you're using the fennel rub, pure oak is the way to go. Very Euro. Figure about 1-1/4 hours/lb for pork to a pull temp of 195. During the last hour or so of cooking glaze the pork with a 50/50 mix of bourbon and maple syrup.
If you don't have a probe or instant read thermometer, the pork is probably ready to pull from your cooker when the bone wiggles so easily you sense it's ready to fall out. When the pork is done, wrap it in saran wrap (better than aluminum foil) and let it rest in a properly prepped dry cooler for at least 2 hours.
Meanwhile prepare your barbecue sauce. Most folks like Carolina, vinegar-based sauces. Red is the most popular, but I like a sophisticated twist on a mustard sauce made by combining the following ingredients in the blender.
1 cup cider vinegar
1/2 cup dijon mustard
1/2 cup mayonnaise
1/4 cup real maple syrup
2 tbs bourbon or sour mash whiskey
2 tbs chipotle hot sauce
A few turns of fresh ground black pepper
1/2 cup oil
Mix everything but the oil. Remove the top, and with the blender running add the oil in a thin stream until the sauce starts to emulsify. Stop pouring when the sauce sets up. You'll see it, it's not subtle.
I'm sure you know there's a very good forum on the Stumps site. You may not know that there are a lot of Stumps owners, a Spicewine owner or two and at least one Backwoods owner participating on the National Barbeque News Forum site. You may be able to get more general cabinet and Stump specific information over there.
You'll probably get a lot of recipes besides mine over here. So you'll have a lot to choose from. Good luck, and let us know how it turns out.
Rich