Thank you, Barnoe.
1. Don't get distracted by comments about fuel stops. It's your holiday and your GPS device, add whatever you like to it and use it just as you want to. The fellow won't be there with you on your holiday when you want to go looking for fuel, that's for sure. That being said, Spain is not the Kalahari desert. There are lots of cars, whose lots of owners must buy fuel somewhere reasonably close to where they live and / or travel to, without too much difficulty. I toured for a while on a bike with a 14 litre tank, which gave a range of about 140 miles; forgive me for mixing the units. If I can do it on 14 litres, anyone can do it with their uber GS / GSA, trust me.
2. Now to the much more pressing issue. I have downloaded your GPX file into BaseCamp on my Mac. I have also updated the maps on my Mac and Nav V, so that they matched yours, just to remove the possibility of mismatch issues.
a. The file consisted of a route and a track.
b. The track displayed perfectly.
c. The route displayed straight lines, between A and B via lots of announced via points (10 or more) no doubt created when you shaped the route in My Route.
d. I sent the track and the route to my Nav V. The track displayed perfectly. The route displayed but it had two problems, being:
i. It was straight lines.
ii. It took no time to go from A to B.
Clearly something was wrong.
e. As a quick way of saving the situation, I summoned up the track on the Nav V and asked it to convert it into a route. This took a little while but the result was successful. I now had a route on my Nav V, fully drivable A to B, Rochdale to Hollee, 145 miles in 3 hours 35 minutes, just as you intend it to be when you created it in My Route.
f. I then went back into BaseCamp on my Mac and asked BaseCamp to recalculate the the route. This it did successfully, the magenta snapping onto the roads exactly. It matched the track. I. short, as near as I can tell, perfect.
g. I then sent the recalculated route to my Nav V and imported it into Trip Planner. It displayed properly. Rochdale to Hollee 151 miles in 3 hours 20 minutes. Good enough.
h. Then I changed all the announced via points (created when you shaped / created the route in My Route) into unannounced shaping points, which also worked perfectly.
CONCLUSIONS
A. The track created by My Route is perfect and can be used on the device as a track or successfully converted from a track into a route, from within the device itself. That alone would have saved your holiday.
B. The route, as provided by your shared file, if sent sent straight to my Nav V, gave only straight lines. It needed to be recalculated.
C. Recalculating the route in BaseCamp resulted in a perfect route which, when sent to my Nav V, was perfect.
D. Using My Route was the start of your problem. I am certain that had you created the same Rochdale to Hollee 150 mile route in BaseCamp from the start, none of this would have happened.
E. You could have saved yourself by using the track.
F. Recalculating the route in BaseCamp would have meant that a perfect route Rochdale to Hollee would have been sent to your device.
G. Depending on how your used your GPS device, how it routed you when you hit GO, will depend on a number of factors; too many list here. I can though imagine why it routed you directly to the end point (from wherever it was you happened to be standing at that moment) by the fastest route, which was probably nothing like the route you had created. If I am right in my guess, that is simple user error, down to nothing maybe nothing more than you possibly choosing the end point as your destination. The device would then do just that. In other words, you have asked the device to: "Take me from where I am standing now, to the end point, via roads you (the device) chose, as dictated by my preference settings". So it did exactly what it had been told to do by its master, ie. you.
G. It's all a mix of two different softwares (My Route and BaseCamp) which we see creating problems quite often, along with a dollop of user error. The latter we see quite often, too.
H. It is all quite saveable, once you understand why the problems have occurred.
PS I have series of screen shots, which I can insert to show you the various stages of the points above.
PPS You'll have noticed that there was a lot of recalculation and / or calculation involved throughout the stages above. Contrary to Giles' theory, none of these recalculation processes altered the route, other than to make it workable. It was all quite safe. Indeed, had the recalculations not been made, you'd have been stuck with the straight lines or been forced to use the track. In short, recalculation in either BaseCamp or from within the device itself, saved the day. Recalculation, when going off-route, is another matter entirely.