The E30 doesn't play very well with Mapsource. To get a Route from Mapsource to the E30, save it as a GPX then transfer the file to
[mSD card]\Garmin\GPX\
via the file manager, it seems to me to work better that way.
I am playing with my new etrex 30. trying to load a route from Oundle to Manchester. I created the gpx from cyclestreets.net, loaded it into basecamp and then exported it to the etrex 30. The route on the etrex is now truncated and only holds the first 70km. If I save with 50 or even 250 points then the route is not detailed enough as it traverses through built up areas :-(
Should I just follow tracks for long routes?
It's unclear whether you want to avoid the built-up areas, or whether you want to traverse them and therefore need lots of turn instructions?
On typical UK lanes (quite a dense network) if you work your way from one place to another turn-by-turn, you'll get a 'turn' no more than 1 per km on average, probably less than that. That means you can define your 200km-ish trip with about 200 points, give or take. You can use these points to avoid Loughborough and Derby etc or to go through those places.
There's no 'routing' or 'navigating' involved if you do this, you just follow the instructions you've already programmed in to the GPS, from turn to turn, up to 250 per Route.
If you choose to use a Track, the same applies, no 'navigating' involved, and you have (on the E30) many more points to play with so that the line you follow closely matches the shape of the roads.
If you want the GPS to navigate for you, then your Route is limited to 50 points, but in practice these can be several kms apart each, so the end result is much the same. Plotting a 200km route across the middle of England that is absolutely nailed down, should only take 30 points or so.