Yes, if I understand correctly, @Southerner won’t have any circuitry on the PC boards. He is simply using the raw PCB material to construct an enclosure. This is a mechanical design task, so a mechanical design tool is probably a more efficient choice than the KiCAD toolset. I have used LibreCAD. Even for superficially “simple” board outlines, features such as “snap to”, ease of defining a corner radius, and offsetting one object relative to another are quite helpful.
Speaking of the corner radius . . . . when you do your enclosure design, remember that PC board outlines are routed with a circular cutter. That means internal corners will always have a radius (or fillet); they will never be truly square. I think most board fabricators can do interior corner radii as tight as 50 mils (1.25 mm), and some probably tighter than that. If something must butt against an internal square corner on your enclosure, you’ll have to define an over-cut corner to receive the mating piece.
Most quick-turn board fabricators charge “by the design”. If side panels (for example) are mirror-images of each other, they are two different designs and you’ll pay for two fabrication jobs. Consequently it may be advantageous to use symmetry, or even include “extra” features to make the panels interchangeable.
Using PC board material to construct enclosures offers some notable aesthetic opportunities. You can play with the copper itself, the silkscreen, and soldermask to create labels, eye-catching logos or even operating instructions . Somewhere on this Forum there is a thread featuring PC Board Art that may give you some inspiration. (Does anybody have a link to that thread?)