If you cut spar varnish 50/50 with mineral spirits that's about what Tru-oil is. I will say it's a good product and you don't have to buy an entire quart just to finish a stock.
Judge, I think your version of Tru Oil is close but I also believe there is linseed oil in it.
Spar varnish was used by bamboo fly rod builders and still used on bamboo rods that are not impregnated. I have done a few myself and in doing the spar varnish is cut and applied with a camel hair brush. Some of the old makers dipped theirs (Garrison is one).
It takes spar varnish very long to fully cure but it is very flexible and does not crack or peel.
Looks great when used over light yellow silk windings with no color preserver on it, the windings come out translucent and you can see the guides feet.
