G10 is overkill, expensive, and difficult to shape/cut, but I can't think of a better material other than wood. My surround for my engine panel is the original teak
and it's lasted fine all these years, either varnished or with Cetol. I made a lexan
"shield" that covers the gauges and lights down to the glow/start buttons and the key.
G10 is a serious %*$&@ to cut due to it's hardness. It will eat through bimetal blades on a jigsaw at an alarming rate. Buy pack of them if you end up going with G10.
You can get smaller cut sheets
of G10 fairly reasonably on eBay.
I suppose another option is to bed
the starboard with butyl (provided it's thick enough and will compress the butyl) and then cut a rubber gasket
for where the panel seats on the starboard surround.