I guess it would really depend on how far you were planning to travel Dr T.
 
I have heard that condensation can occur in partly filled tanks leading to corrosion and debris in the system. his could lead to costly repairs or a poorly performing engine do you think?

never heard that before -- all tanks generally go from full to less than 1/4 full.
 
I am suggesting that it would be more economical to run from half full to nearly empty as one would be carrying less extra weight arround in the form of fuel, let the oil company move it for us even on a long journey.

I have read somewhere that allowing your fuel to drop TOO low also causes slightly more evaporation of fuel (even though within the tank) as it's more susceptible to this in hotter weather when the temperature increases. The air expands within the tank, and leaks all the more, especially with greater amounts of internal air present when fuel levels are subsequently lower.
However, there also isn't apparently much merit in OVER-filling (as in 'to the brim'). This I can refer to the source, as I have recorded it: The BBC:
"Stopping at a supermarket to get fuel, I obey another eco-driving edict - not to brim the tank, as this adds extra weight and reduces fuel efficiency. I pump in 35 litres (the tank holds 40). £41.26 - painful, but not as bad as before."
I rather think that this will complicate or confuse things, rather than simply clear them up - but that's what 'eco' invariably entails :)