Tank 3D Model

Working on 3D modeling more, I wanted to try my take in redesigning Fallout 4's tank to be more practical without Smooth Renders or Subdivision Surface.
Wanted to keep the design super grounded, practical and 50s yet keeping their twin barrel and nuclear thingy ma-jiggies present. Fusion Core engines in the back are meant to be retractable.
Looking for blender guru tips in how to make sure a face is truly planar without having to resort to Subdivision Surface to stop those weird triangles.