Hi Chaps.
I use a Etrex Vista with Mapsource tweaked to enble "follow road". Even if I inherit a .gpx I usually rework it, setting user WPs at mid points on a road, i.e., not at junctions, then use WINGDB to generate a track (if ICBA). I let the autorouting take me through the junctions, after all, thats why I bought it.
Prior to generating a track I select direct routing and recalc on Mapsource so when I convert the route to track I get the same number of track points as route points. The gps effectively shows the route in both direct and follow road mode.
I run the gps display in autozoom mode so you can usully see the next control or two, so its soon obvious if the gps autorouting attempts to lead you astray for some reason, even if I have not bothered to generate a track.
I post up the Control WPs in red flags, then add in additional WPs as required using blue flags to align the mapsource route to the routesheet. I'd normally use <50 WPs for a 200, so a 200km audax only requires one file. Usully I have the route nailed at 35~40 WPs then add some extra WPs to make it up to 50.
I don't bother with a structured WP numbering system, though I give WPs town/road names as appropriate, so I get a plain english alert message on approach ("30s to wherever").
It's not perfect solution but it works for me.