-
You should still find it’s fairly still near the top of the tank as your clocks should create a bit of a buffer. As has been said write the major town names on a bit of paper and tape it down, I would add the road you leave town on as well (eg 414 Chelmsford; 414 Danbury; 414/1010 Burnham on Crotch).
Have a copy in your pocket and a copy on your phone. If you have a big rear map pocket, shove the paper copy in there with a paper map.
I've gone through sothern sweden with a list of major town names hand written on paper and taped to the tank.
For more precise directions it might be a bit more tricky.
Just get out there. Stop and check your phone once in a while.