I don't have an RV at present, but have traveled with one or multiple GSDs pretty extensively.
Absolutely agree with teaching them to pee on a leash, on command, quickly. Saves a lot of misery standing around at rest stops in the pouring rain or blizzard.
Set up a Dropbox or other cloud-based storage so you have digital copies of all your dog data at your fingertips. I either scan (if I'm at home) or take phone pics (if I'm on the road somewhere) all vet stuff and receipts, and POOF, it goes up into the cloud, saved indefinitely and I don't have to tote paperwork piles everywhere. This is invaluable if you end up having to take a dog to a new vet when you're far from home (been there). You can also provide proof of vaccines and proof of flea preventative at a moment's notice (I've found rentals and whatnot in the southern US have started asking about flea treatments, recently).
Try and raise your dog to not be a picky eater. This is kind of a touchy subject, there are a lot of opinions out there. If your dog truly doesn't tolerate certain foods, that's one thing.... but if you can, rotate some different foods, get a feel for whether or not your dog has a sensitive stomach. Condition your dog to eat what is put in the bowl. Even with the best of intentions, traveling long enough eventually leads to running out of dog food somewhere inconvenient and buying whatever the gas station sells. JMHO.
Like so many people above, I've not had problems with GSDs adjusting to different spaces - tree houses, boats, hostels, hotels, living (literally) in the back of my SUV, tents, hammocks, etc. They figure it out.