It seems a bit odd, servicing German caravans is no different from servicing UK built 'vans. The Chassis & interior equipment are all the same makes. You would probably be better using a mobile service person with the added advantage that you can watch them at work to ensure they do a proper job.
At this time of yr many caravan workshops are booked solid for 2mnths or more so it might be just an excuse to put you off if they don't want to take any more bookings. If the 'van is running ok it might be an idea to leave servicing to later in year.
Alternatively try a trailer workshop. They will be able to service running gear which is what you want for reliable tow & cost is much less than full service by caravan workshop. Many owners do this anyway. Pay for a chassis service & check interior themselves on an ongoing basis.
i have been recommended by two clients to try mobile technician "Boris" on 07981 525 886 of Hampshire County Caravans, to service my Hymer.
So far I personally have not tried him having done my own servicing for decades, but my age is now working against me!
Please tell us how you get on and performance rating. Those recommending him to me were both very impressed.
Dave from Caratechs came round today and did an excellent job, I'm very pleased. Full service and sorted a few issues out also. Now have peace of mind taking to the road for the season.
Highly recommend!
http://mobilecaravanservicingtoyou.com/
. Mobile Workshop Hot Line Dave 07970827585
. Office - Out Of Hours 01344481605 (Answer phone)
. E-Mail dimogen at ntlworld.com / caratechs at hotmail.com