Sorry to disagree with Chef Ray and team, but my experience differs.
You can brine brisket. In fact, pastrami is usually just that: Brined, seasoned, and smoked brisket.
Second, people actually do smoke heavily brined corned beef -- more in Texas than anywhere else.
Third, the fat cap doesn't melt at 180 and move through the brisket. That's false.
The moistening effect comes from denaturing protein molecules, and the denaturing occurs inside and not outside the meat. One group of those proteins are "lipoproteins," which are the bulk of the internal fat. These are different from the fat molecules forming the fat cap. The lipoproteins are delicious, especially when melted -- the fat cap is basically unpalatable and very digestible, except in a very thin presentation.
Leaving the fat cap on will help hold some moisture in the brisket, only because no moisture is lost through the impermeable fat. A 1/4" of fat works just as well as 1/2 an inch. Also, there's no agreement among top competition and professional pitmasters whether the cap should be on the top, the bottom, or whether the brisket should be turned.
Unless you trim the cap extremely close, you cannot retain any seasoning; and it will not form any sort of bark. If you do leave the cap on, all or nearly all of the fat cap must be removed be completely removed before service. You can scrape it off with a spoon.
I'm not selling my methods as the "best," or as those you should use. But I do a 1/4" trim, and season both sides. I turn midway through, because even though my pit is well tuned I like to make sure everything cooks evenly. I put the brisket on the board, fat side up and check to make sure the fat isn't too thick. If it's more than a 1/4" in any area, I remove it completely.