Here's a good article on spare rib preparation, trimming them St Louis style is up to you. The most important thing is to get the membrane off.
I don't rub mine until I am getting ready to throw them on the cooker, if you rub too far in advance you can sometimes end up with a hammy taste (depending on the salt content of your rub).
Cook them between 225°F and 250°F for between four and six hours checking them periodically after 4 hours to see if the meat is sliding up the bones. Once the meat has slid up the bones you can try a bend test to see if the meat is ready to come off, otherwise pull two bones in the middle of the rack and see if the meat tears fairly easily, if it does, they're ready.
Sauce them at the very end so the sauce doesn't burn.
What type of pork roast is it? Butt, picnic, loin, fresh ham? Depending on the cut, you'll need to cook it a bit differently (at different temperatures, and to different internal finished temperatures).