Mick, I reckon you'd have been fine with the tires you had, just bad luck. The best option for your bike would have been something like Tourances, Anakees and they would puncture almost as easily as road tires.
What seems counter intuitive but should be done is to let your tires down a few psi, maybe mid 20s for your bike. It helps ride the gravel a bit better and reduces the risk of punctures.
As I said though, sometimes it's just bad luck, sharp stones bits of metal and the like. I picked up a 25mm slash in a dirt tire out there one time and needed about 10 rope punches just to limp back to civilisation. Next time I ride out that way I'll take a few of those plugs that spread out from the inside.
I hope you guys have another go at this, it's a ride I'd like to do sometime as well.