Check the controller manual. Some of the "advice" here is dangerous BS. For instance, Morningstar, Renogy, Midnite Solar (and I'm sure most manufacturers) all advise that a fuse or breaker be installed in every circuit (battery, solar, load). If a properly sized protective device opens, it could have saved you from more serious issues than a damaged controller.
The wiring length/voltage drop won't keep your battery from getting a good charge. You will lose a bit of efficiency, but the battery will charge fully (the current and therefore the voltage drop will taper off as the battery gets full). If it's a PWM controller, it really doesn't make any difference whether the controller is near the panel, the battery, or somewhere in between. Using a controller lacking remote battery temperature sensing is a bigger concern than voltage drop as far as proper battery charging goes.
Wiring to the battery connection at your converter is fine. You can check to see what gauge wire goes from there to the battery, and you want to use the same or thicker from the controller to there, along with an appropriate fuse/breaker near the controller.
Also, it's going to be just the charging current going to the battery - any going to devices gets distributed straight from the panel, so that eliminates some of the inefficiency due to voltage drop you would have if it were wired direct to the battery.
