Now, that's a SMOKER!!! Great concept!!! Hot and cold smokes all in one cooker from a hard-wood fire...I envy you.
If you're brisket is trimmed pretty lean, it can't self-baste during cooking. Injection I stay away from, personally, just due to creating a compromised muscle which should be handled to a more stringent guideline for food safety...(see HERE). Marinates I haven't used much either, and brines really aren't a big thing for beef (more for poultry or pork).
Here's the thing about lean trimmed meat: with the fat-cap removed you have more surface area for smoke and BARK. I started experimenting with lean trimmed meats a few years back, wanting more smoke and bark, while maintaining a naturally moist finished product...and came up with this (long read...get comfy with your favorite beverage nearby):
Wet-to-Dry Smoke Chamber Method
Every kind of meat I've smoked using this method, from pork butt to pork picnic, pork spare and baby-back ribs, and brisket (among others), has yielded very good results. The principles of the method are described in detail, leading to what I've used it with, as well as some Q & A from other members at the bottom of the article.
Hope this gives you some insight on which direction you want to try next.
Give me a shout if you'd like some help figuring out how to implement this in your rig, or to determine if this is the route you should go...it may not be for everyone, but some don't like the taste of brisket fat, I've found...that's just one of many benefits to smoking lean-trimmed meats.