Does anyone know who makes battery covers similar to the one in the picture? Thanks!

You might check with Dustin Carter ( Carters power boats ) in Broken Arrow, OK

Very easy to make those. Carter has Vincent Custom Paint do the graphics on those I believe. All you need is a flat piece of aluminum cut to your battery box outer dimensions, most hardware stores have the threaded nuts you can use to extend the threaded battery hold down rod and then pick up the screws of choice for the cover (I think the allen head screws look the best). Drill and bevel the hole and then send it off to paint. Be sure to use stainless hardware.

Thanks!