After a few weeks of testing I have hopefully narrowed down the problems with my latest WR703N setup, where it continues to reset the internal USB hub. I have plugged in an additional USB hub (un-powered) and plugged the USB flash drive and GPS into that. The GPS works straight away and the USB flash drive (/dev/sda2) doesnt have the same I/O and filesystem errors. Will perform thorough testing through out the next week and see how is goes.
In the previous post I thought it was power to the internal hub, so I have tried adding a 100uF capacitor. It initially started out being a r/w lock on the Sandisk USB flash drive, which I think was a result of a poorly constructed USB hub.
Found a USB hub that can be powered via an extra USB power lead and like usual results look good but time will tell.