Anyone know what is the best way to protect painted wood from the elements? Normally on bare wood I would use spar urethane,but they say not to use that on painted surfaces.

A good coat of exterior grade paint goes a long ways to protecting wood. Sun, water, and everything that lives on wood constantly attack the paint and any wood underneath it gets to. A coat of wax won't hurt. Spar varnish is not as good as paint at protecting wood. The problem is that the UV in the sunlight passes through the clear coating and still destroys the wood under it.

Hi,
If you have put a couple of coats of good paint on the furniture, then that is the protection the wood needs.
I have a 6 ft. privacy fence around the back yard; painted it with two coats of good paint. It doesn't need painting again for years. Some of the sections are 30 yrs old. Even though it was "treated wood", paint still makes it last much, much longer.
If you notice any cracking, chipping, or anything else with the paint, then a light sanding and repainting might be in order. It should last for years. Best of luck.