Have a read of this if you haven't already done so
www.antiquerestorers.com/Articles/SAL/rub.htmHaving read this, I realised it is a finish I have done (on a homemade coffee table). It was a long, tedious process that looked great when finished. I am not sure if I would put the time and effort in for exterior use. It would look a treat, but I don't think it would make the varnish last any longer.
Have a good read of the link above. It does make mention that standard varnish is hard to rub.....