exterior finish

so im amking a sight form timber routed out. painting inside the routed bits but want to keep teh rest natural.

is tehre a varnish that will stand up out doors?

Marine varnishes, though they need recoating every year or so

what about fiber glass resin?

Try this link to various epoxies for marine use.

http://www.westsystem.com.au/

There is one technique to paint the epoxy (with the uv stabilisers) on to the timber and when cured paint the marine varnish.

When you need to refinish the varnish you only sand back to the epoxy. It works for boats.

Hope this helps.
Cheers,
Jim