Hi Antonius,
I don't think this technique has to be restricted to only sheetmetal models.
You can pattern the --\\-- fill element, then merge them at once (just make sure they don't overlap) and you can use the find tool to select the quilts at once:
After that, you can trim away the outside, then merge the flat grille with the outer part of the panel. Then you can thicken this surface to make a solid... Also note this uses "Geometry Pattern" so it is fast.
