Just saw this post. What did you end up doing?
I've done several exterior wood projects over the last 15 years. PT lumber, white oak, mahogany, okoume, sitka spruce, fur, teak, western red cedar. I've tried so many thing and cannot count the all. Conclusion, nothing lasts 2 years. And dispite what "they" tell you, the continual reduction in VOC content make it worse, and water based just isnt there yet.
If you want clear or amber "varnish" try the top end marine spar varnish. It will cost about 5x what you paid for the Minwax Helmsman. On boats, you usually put on 7 plus coats, and your're still redoing it after 5 years.
If you go oil, like someone said, stuff grows in it.
I did one picnic table in western red cedar several years ago with the latest an greatest mix of African and synthetic oils and pigments and did a second set, but just painted. The oil table looks good for 1 year and looks like crap by the end of the 2nd year. The painted ones look as good today as they did day one.
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