I'd agree with the above. Scuff the surface of the marble/granite piece used with silicon carbide (black) sandpaper if you use that to give the glue a good grip. May not be required, but it would only help things.

I had a bunch of quartersawn kingwood and cocobolo on hand, though, that wasn't really wide enough to use productively (about 3 1/2 inches wide and an inch thick), and used that. It has nice mass and doesn't move when it gets wet.

If I were to use maple, i'd want it to be quartersawn from a tree that grew straight, though if it's sealed, it probably wouldn't move.

Walnut is a well behaved wood, one where quartersawn isn't quite as critical, but it's not as heavy. I have at least one stone (thinking, can't remember if more...) on walnut sealed with shellac, that has stayed flat, and it is flatsawn wood (no special type).

It may be that we don't need to be that critical of wood - I've seen a lot of ratty looking bases on old japanese stones. I don't intend to find out on my stones, though.

Anyway, I've always used epoxy, too, just not marine grade (devcon 2 ton epoxy would be fine). It gives a nice gap fill and bedding to the stone and is still strong. I guess I've been using epoxied stones for about 6 years under very heavy pressure sometimes (when working over a vintage woodworking tool) and had no issues.

Another option, btw, that's easy to score and snap is 1/2"+ thick glass. Wood is the easiest to work with, though.