i too evolved to using sand in the water pan (not the original Weber pan, IIRC, Brinkman, maybe?) but stopped doing it because A: it was too heavy and doing bad things to the tabs it hung on and B: grease would get past the foil, & into the sand, then go rancid. instead, i just saved up aluminum foil used for other things, then crumpled it up and covered with several layers of foil over the top. w*rks just fine.
other mods i'd suggest are: a second charcoal grill, placed at 90* to the orientation of your first grill, to hold coals in place longer. you can wire them together if you want, but it isn't necessary. a charcoal ring to hold your pile together is also a good thing, and, if you cut both ends out of a 1# coffee can, and place it in the center of the ring before you add the charcoal, you can then put your lit charcoal in the can, then remove it with a pair of channel lock pliers, and voila! you're using the Minnion Method of fame & legend.
Top vent wide open, control the temp with the bottom ones. once the smoker is at operating temp (225-250 for low & slow) you should only need 1 just a little open to keep things chugging along. i just put a dial thermometer in the top vent to check the cook temp. if you have a Polder or equivalent, you can run the probe wires out the same way, and neither seems to bother the cooking process.
no idea why your shoulder was dry, but i usually do mine overnight, so i'm not sure what recipe you were using. as long as the meat pulled apart properly, it was cooked right, and remember dry pulled pork can be remedied with apple juice or cider in judicious amounts.
hope this rambling message helps!