Welcome Gwen! I'm late to the party, but I'll add my $0.02, to the many good observations others have shared. I've camped all over the lower 48 and bits of Canada and up through Alaska. I've used all types of bikes from standards (Triumph Bonnies, BMW Roadsters, etc., Sport Touring (aprilia Futura, Triumph Sprint, BMW RTs, RS and S1000XR), Adventure bikes BMW GSAs, GSs, Guzzi, KTM), and Baggers (Victory Cross Roads, HD Road King), and will do more of the same on the R18 (roadster-bagger-?). I have ridden many miles on all types of roads with all of them, but there are obvious limitations as to their design(s). Be honest with yourself as to your desires and limitations and try to get the most comfort and fun from whatever you choose. "My favorite bike is the one I am riding" is a simple truth for me and as there really are no bad motorcycles being offered today it makes it a great time for us to enjoy riding. BMW is very good with offering a variety of different seat height options as well as low suspension models pretty much across entire range. Weight and deep sand will see you working more and smiling less so if there is a high likelihood of going to those conditions often I would recommend not going it alone as getting stuck and/or lifting the bike from a dirt nap(s) would get old quickly on any bike and the R18 is very heavy regardless how low that weight is carried. Hard pack or maintained gravel roads like in many National Parks, etc., are very enjoyable with reasonable riding skills and when dry I wouldn't hesitate to ride them on any bike. In the early years I packed like a 2 wheel "Beverly Hillbilly" truck with so much kit I didn't need and over the years I have replaced gear with more appropriate "backpacking" size and weight items and my clothing has been streamlined too. There are washing facilities in most campgrounds and our modern riding gear functions so well it allows cutting down on many of the extra rain suits, etc. Anyway, the RT and GS/A type bikes are a great tool for serious touring and back road exploring with both offering large petrol capacity, luggage options and so on with them being very well polished apples, maybe almost too polished? I really like the "Heritage" R line and was surprised it took so long for BMW to finally offer cruise control and tubeless rims on the lovely R9T and to be honest it is a huge $ negative to correct the same items on the first R18s that only had the tube tire option offered and/or no cruise control. I am extremely happy to have the R18 as it is a genuine hoot to ride be it on the Interstate or at a surprisingly quick pace on our lovely Appalachian-Smoky Mountain backroads and they're just a beautifully built motorcycle! BUT, with the R9T improvements I would have picked up one of those if not for the price incentives on the R18. That all said, luggage will be a challenge on those as well and I use a good waterproof "duffle" I can strap behind me that carries camping gear, "shaving kit" and clothing and I use the smaller saddle bags for the extra tools, gloves, snacks, etc., that I can get to easily and I like to have at hand be it a short ride to lunch or on a longer touring run.
As mentioned above, BMW is great with test rides so if possible get with a shop that has a bike available and they will help you with your decision making.
Good luck!