I'm originally from Sheboygan, Wisconsin, ground zero for Johnsonville brats, the cube steak steak sandwich, the "hard roll" German-style bun and the butter burger. Not a huge secret to them, although I wouldn't worry too much about seasoning (other than S&P) or forming much of a crust. Slow cook 80/20 and assemble as you described!
~ Scott ~
Blue Weber Performer + Craycort CI • Brick Red Weber One-Touch Platinum • Weber 26.75 Kettle • Akorn Kamado • ET 732 • Record-crushing ORANGE Thermapen • UDS In Progress