A view from the other seat...
On my first cross country navex my instructor very kindly flew the a/c and just asked me to navigate. Don't know whether it's simply because I'm a particularly slow learner, but it certainly gave me the opportunity of concentrating on what it is that I was supposed to be learning and I think I got a lot more out of it as a result. Consequently, when I next went on a navex and had to fly as well as navigate, whilst I found the workload somewhat demanding the navigating wasn't as daunting as it might have been.
Just a thought.