I have several rifle stocks that were left bare on the inside by the manufacturer. What would be the best thing to seal the wood from moisture.

Spar Varnish. I've used it many times.

Any finish is better than no finish.
Spar will work fine.

-Spencer

Yup. I use McCloskey's marine spar varnish because that's what John Barsness recommends, and also because that's what they had on the shelf at the local hardware store.

Going by the looks of the stuff, I'd be willing to bet that the insides of my stocks are more waterproof than the outsides.

Any good finish thinned 50% with mineral spirits..In a properly bedded rifle if you use straight spar, then the barreled action will probably not go back in the wood..and even on a factory rifle 2 or 3 coats of thinned is much better than straight spar or any finish with the exception of a few finishes like Flecto varathane that are water thin to start with...

Apparently I've never owned a properly bedded rifle...

Noel,
Hopefully you will someday, hang in there.

Do you guys get Weather Seal or similar products over there? Its sold in DIY shops here in the UK and its meant for exterior woodwork or stone. Has a very, very thin consistancy (like water) and simply soaks straight into untreated wood to waterproof and stablise it.

I give the interior of my stocks a couple of coats of that and then use a decent varnish...

Regards,

Pete