Good news Deano.
Here's the reasons behind the cap failure issue:
The coolant system in the F and TF is pressurised, this is because (basic physics) pressurised fluids have a higher boiling temperature than non pressurised fluids. To control the pressure in the system there is a very simple pressure release valve built in to the cap on the expansion tank. It consists of a rubber sealing ring and a spring loaded circular plate. The idea being that as the pressure increases the spring is forced open and some air (from the top of the expansion tank - this is why you should never fill it beyond the maximum mark) is released.
The problem is that the spring, over time, relaxes a little and also with the constant trickle of red hot air past the sealing ring the rubber perishes somewhat. This results in a gradual lowering of the boiling temperature of the coolant until it boils over.
That's the bad news.
The good news is that the caps are VERY cheap - i replace mine annually and always carry a spare (got two in the boot of Scarlet as i type!) A couple of pounds each year is a small price to pay for peace of mind.
Deano, good to hear that it wasn't HGF, but i am a little concerned that you may be being a little extreme in your proposals for dealing with it. I understand your worries mate, but as (i think) James C said earlier in the thread it'll either go HGF or it won't and until it does there is little point in trying to fix it. Invest in a B+G alarm system to give you a heads up should the worst happen, join the AA or similar, save your pennies and then if it does go bang, at least you will be aware before hand and can switch off to minimise any damage. By this time you should have enough money to fix a real problem (rather than an potential one) and can also invest in the Land Rover HGF cure (that i supposed to be a permanant solution).
Besides, you have an expensive mobile phone bill to Steve and i to pay for mate!! Ringing a mobile in Sweden to get a breakdown recovery number in the UK is an expensive way of getting rescued mate!!