Note from editor of Mosel Wine Newsletter.

Dear Richard,
Sorry for the delay in our answer, we are nose-to-the-ground flat-out busy with all sorts of things but let me guide you through.
It sounds like a great trip, just letting one float from Trier to Koblenz!
David and I usually stay either around Bernkastel when tasting in the Middle Mosel or in Ayl, when "doing" the Saar, Trier, Ruwer. None of us ever stayed overnight around Koblenz.
We look for simplicity (a bed for the night and a good hearty breakfast). In this category, we can happily recommend the Gasthaus Karl Erbes in Ürzig or the one held by Kees-Kieren in Graach (both have websites). You may want to check if this fits with the boat trip and where it halts: For your information Graach is roughly 1 mile away from Bernkastel but Ürzig is a good 5-10 minutes by car (2-3 miles). Both are around E30 per head, so really cheap.
Should Ayl be ok for overnight (it would mean taking a hire car tough - it is about 15-20 minutes away from Trier), then we would recommend the hotel held by Peter Lauer (see also the website) but it is a little bit more expensive (around E60-70)
Also keep in mind that july is summer holiday season, so I wouldn't wait too long before booking.
On the wine and food front, some recommendations:
- There is a very good shop in Bernkastel with wines from all the big names at essentially ex-cellar prices. It is called Weinhaus Porn (yes, I know, strange choice but the lady is really called Porn).
- In Trier, there are two places for eating that I would recommend, because both have a terrific Riesling wine list. More upper class is Schloss Monaise, more typical German (good hearty food) is Eurenerhof. Both have websites.
Hope this helps you further and wish you a most enjoyable trip,
Best,
Jean