Firstly, you are not correct in saying that lorries in general must not overtake on two lane autobahns. This only applies where signposted. On certain stretches this overtaking ban is extended to cover cars towing trailers as well (again, this would be signposted separately).
Secondly, the speed limit for lorries is the same 80km/h as the standard speed limit for caravans, so there is theoretically no reason why a caravan should hold up a lorry.
Often, however, frustrated lorry drivers are under such pressure of time from their employers that they ignore the 80km/h speed limit and drive at the 90km/h that the speed governers allow. As the lorry drivers know that cars, even when towing, are also capable of going at 90km/h, they can't understand why caravans should be holding them up.
Lorry drivers are generally well informed where speed traps are so they just go at 90km/h unless the gravevine ahead has told them to expect radar. That's why I tend to join the happy crowd of lorries and drive along with them unless their speed drops due to gradients etc.. That way, nobody gets upset; I drive a little faster than I should but in the knowledge that the lorry drivers know what they're doing as well. In general, I therefore set the cruise control at 88km/h. If there aren't any lorries about and I happen to get caught (which I haven't as yet in almost 20 years of caravanning in Germany), I'd still be right on the limit of what the police allow as a margin. Besides, except in extreme circumstances, German police do not normally stop you but send the summons to your home address later by mail.
Also, as a driver of a right hand drive car you're lucky because speed cameras are set take a picture of the person sitting on the left. By German law, not the holder of the car but the driver is responsible for any infringements so the face of the driver must be recognisable. The photograph of a right-hand drive car would show the front passenger so the police would not be able to prove who was actually driving. It must not show the person on the right as well as this is deemed to be misuse of personal data (it could be someone you wouldn't want your wife to see should she open the letter from the police)
So don't worry too much when driving in Germany. Just drive sensibly as you would elsewhere and nothing will happen.