Why not use something other than Basecamp? There's a recent thread and the chap struggling with a BMW Garmin thing has found MyRoute has helped get some routes for his trip.
I have the Zumo 390. I just use trip planner on the Zumo itself, getting mapping detail from Google Maps for waypoints from my phpne, tablet or laptop. I break a trip down into single or half days where routes are pre-planned. This also means I can easily knock up a route sat in a hotel after checking weather reports during a trip, as I am fully familiar with the Zumo and its little ways.
If someone ever writes a book about how a software user interface should not be, Basecamp would probably tick of most of the boxes.
However, if people endure the pain and keep using BC, eventually, it will work at a level we may be able to live with.
I have tried several other options, such as MRA and other similar programs. And the planning is soooo much easier in most cases.
But there is a catch, which force me to revert to BC every time.
Most of these programs draws their route as a track. This means that a day of decent driving may contain several thousand waypoints. Some of the programs do offer to turn the track into a Route, as a GPX file. But in many cases, the generated route contains LOTS of waypoints.
This still looks great on the PC screen. Hower, as Garmin GPS will only handle a limited number of waypoints, more often than not, the wonderful looking routes comes out different when loaded to the GPS. The GPS handles the first waypoints, and up to it's maximum limit. And then the route stops.
There may be some smart ways around it that I have not yet discovered, but it boils down to the reality. Even as cumbersome as the BC may be, it takes a shorter time to plan a ride with some distance using BC rather than using MRA (or similar) and then modify the generated rout into something useful.
Splitting the long ride into several shorter routes may overcome some of the issues, but then again, that is a pain too.
If using the phone, these limits may perhaps not apply, but until further, I'm not ready for using the phone yet...