Hello, all. Just wanted to share something I found that fellow RG300 users may find useful. If anybody is looking for a nice carrying case for their RG300, this one, originally intended for portable hard drives, fits the RG300 absolutely perfectly, and it's only $8:https://www.amazon.com/gp/product/B00Q59EQ3C/
(Screen hastily blacked out to hide reflections.)
The RG300 itself fits in the right side like a glove. The case is big enough that you don't have to cram the RG300 in to force it to fit, but also tight enough to keep it from banging around inside, and the elastic straps keep it held down without putting undue pressure on the buttons. On the opposite side is a mesh pocket that's perfect for holding a few accessories. I keep a short USB-C cable, a screen cleaning cloth, and a pair of earphones in mine. In the middle is a soft padded flap separating the two sides of the case, which keeps the screen safe from being scratched by anything in the other side.
Just a little something I wanted to share in case anybody might find it useful! There are lots of these cases on Amazon in slightly different sizes, but I don't think anything could fit the RG300 any more perfectly than this.