Generally after three hours of cooking the meat has accepted all of the smoke that it's going to so just go ahead and wrap and work on preserving moisture at that point. It probably wouldn't hurt to inject with some low sodium beef broth and maybe do a dry brine. Dry brining is simply sprinkling liberally with salt the day before the cook. The meat will first expel water and you will see the meat get noticeably wetter, but then the water and the salt will be pulled back into the meat locking the moisture in. Here's an article on the subject, this also works really well for steaks by the way! Good Luck!! http://www.amazingribs.com/recipes/r...y_brining.html
P.S. I would leave the fat cap on or at least 1/8 inch of it. Depending on what type of cooker you have you may want to use the fat side as a heat shield and it also helps form that nice sticky bark that adds so much flavor!