Hi Peter!
All congratulations your way on what is a legendary Thorn tourer -- the eXp! I remember last summer when you had decided to sell your motorbike and look for a Thorn. Boy, did you ever find a good one! Can't wait to see photos.
I have used a Garmin Oregon 400T for my touring needs, like it very much, and chose it for the same reasons. It is similar your 450T except for the software, triaxial compass, and more easily daylight-readable screen.
You're not alone in your frustration! Garmin's included documentation is woefully poor. If you are new to the units, the learning curve is pretty steep and the lack of included instructions sure doesn't help. The units are great once a person catches onto how they work.
WikiSpaces has a wonderful guide devoted to the Oregon Series including the 450T here:
http://garminoregon.wikispaces.com/Additionally, these 450T-specific resources might prove helpful to you:
Garmin Learning Center Training Videos
http://www8.garmin.com/learningcenter/training/oregon/Garmin 450T tutorial videos on YouTube
https://www.youtube.com/playlist?list=PL32FA7E1CCCA05B6EWhere do I start? (with BaseMap questions)
http://forums.gpsfiledepot.com/index.php?topic=1447.0Garmin Basecamp Tracklog Tutorial
http://gpstracklog.com/2012/02/garmin-basecamp-video-tutorials.htmlI hope this helps, Peter. If you have problems after the above, give a shout.
Best,
Dan.