This is a "shell" that I have drawn, colored in, and scanned. It's a large .tif file that I use in Photoshop. I may resize or rebalance the color, but what you see in a finished cartoon is a scanned shell with text added.
I came across this strategy by accident because the most difficult part of all of this for me is not the drawing, it's the lettering. By using Photoshop, I can speed up the process, reuse a drawing, and really edit and refine what goes into the panels.
Here are two examples of this used in the same shell.
That's all there is to it.