Best advice , don't restrict yourselves to 'Bikers Hotels ', we have been touring on the Continent since the mid 80's and since 2000 go down to the Alps every year taking in Belgium , Germany ,Austria,Northern Italy and Switzerland plus other trips to central and Northern Germany and have NEVER had any problems with accomodation.
We have found some fantastic smaller hotels to stay in and most have either had secure bike parking or insisted we park in their own private garages. Some we have only visited once passing through whilst others we have visited on repeated occasions and the owners have become and still are good friends
I could list 50 or 60 hotels all of which I would be more than happy to go back to, on the Continent motorcyclists are not looked down on and you are a paying customer the same as the person next to you.
We have visited small German villages on the German Baltic Coast that were in the old East German area where everyone wanted to try their English out on you and talk to you about the area they live in .