[pletby]

Here's how I fashioned the grille block using coroplast and some vinyl I had kicking around. The vinyl strips were capping to cover screw positions on a window unit.

Tiny wooden blocks were a bit of a pain to cut, but easy to install.

Painted ordinary screws to match, but after a few years they've rusted badly so will replace with stainless. If you don't live where salt is on the road to melt ice this might not be necessary.

Used a piece of wire with a 90 degree bend to secure a sliding vent cover so I could set it at any degree of open/closed. Just pull wire up, slide, then push wire back into corrugations.

In the final product you can see I could have used another coat of paint. I'll save that for Mk II to be in production later this year.

Notes: Plate interferes with the opening a bit. Might relocate plate. Coroplast takes hits from road grit in the summer, but perforates in the depths of winter through the first layer. Over time this is becoming an issue. Still after 2 years it looks not too bad.