The varnish took ok over the cuprinol. I gave it three coats with a smooth flatting down between coats. As for giving the wood work a good scrubbing down a couple of times a year, i think you will find that its impossible to get at the underside of the sill boards once the wings and exhaust have been fitted.
If you wanted the wood to breathe theres no reason that you cant leave the inside faces of the ash frame unvarnished. I have used an underseal on the plywood wheel arches as they receive a bit more stick than the sill boards (protected by the wings)
