Pb84 - thanks! To be honest, the distance isn't the issue (3 and a bit hours after spending some time sightseeing around mull), and the nav isn't particularly difficult (plan it on skydemon, fly a bunch of straight lines, and cross check map to ground to GPS).
However I agree with some of the posters on here that a PPL just doesn't prepare you for doing longer trips.:There's no way you can do this just by dead reckoning, PPL fuel planning (at least in practice) seems to involve checking that we'll have half a tank left and saying OK, and no one ever taught me to use the red lever as anything more than an on-off switch.
I've been lucky to fly with some excellent instructors, who have taught me a bit about how to deal with mountains, red levers, GPS and other such esoteric topics...
On a completely different topic, I encountered mountain wave for the first time today. 30kt winds over the welsh hills, there was at least a 500fpm rate of climb/descent. I was surprised that each wave seemed to last for about 10 miles - I'd always thought they were less than a mile wide.