Progress update:
I downloaded 'Viewranger' mapping software to my Samsung mobile. Paid out some money for what seem to be half decent 1:25,ooo Spanish topo maps and went for a drive. Please appreciate this is a quick test on the mapping software, the phone screen is way too small for use when on the move, depending on my recent blood glucose numbers my eyesight being somewhere between bifocals and binoculars.
The phone has the typical built in GPS so no connection issues there. As the maps were on the phones SD card, I turned off the phones data link, this will ensure there is no additional cost to my mobile phone bill, and with no 3g/4g coverage they would still work...and they did. The result is not too shabby, there seems to be a short lag in updating my position when off road, out on the more open roads this is not so noticeable.
The phones position in the car does not help here, the more sky that can be 'seen' the better the sat fix, so understand there are improvements to be made. This may also help when choosing from the android tablets I have been looking at, a cheaper unit but with a larger screen may not have a built in GPS but, this would mean the use of an external one (which I used on the TB), would have a better view of the sky and thus improve accuracy/update time. This would mean keeping additional hardware, but given the tablet will have no other use, it will live in the 80 glove box unless in use on the way to, or on a trail, so the GPS can stay with it.
I looked at a couple of sizes, 5" it seems is ridiculous (well, so I am told), so 7 or perhaps 10" is the way to go? It was mentioned earlier about reflections, so I wondered about suspending it from the overhead console where the altimeter and sub fuel gauge (not used) console is sited, try to think of the better airlines that have the film screens in the ceiling, not on Dan Dare airlines (you know the ones with the outside toilets) so, a screen that could clip into a carrier, and being higher up it would be in the shade so the image would be easier to see, trying to find an android screen with 'nit' count info is quite difficult.
The screen may hang down too far even in portrait view and obstruct vision when in use, so looking into this at the moment. When a choice has been made on the tablet purchase I will post back, thanks to all who have contributed.
regards
Dave