Should be pretty easy to make a somewhat
weatherproof one too... print out your design on heavy stock paper, attach to rigid cardboard or plastic, and wrap tightly in clear packing tape or plastic wrap.
The latter two steps I came up with after Illinois redesigned its temporary plates a couple years back... they went from a interior window sticker to an exterior cardboard plate that would always fall off after getting wet.
I went through 3 replacements before my real plates arrived! And some consultant was probably paid millions to come up with that idea!
My tax dollars hard at work!