We make a pen, using three ex-pens that is just a bit larger than our awning. Unless we are on a REALLY clean site, like clean gravel, or grass when it's not going to rain, we put down a patio rug. The dogs mostly stay on the rug... our chairs and their beds are on it. They will go off the edge to potty, but they don't get too dirty.
In REALLY bad weather, I keep them in to pee (litter box) When they need to poop, we let them out into the pen and pull back an edge of the rug under the awning. USUALLY they will use that dry area... They don't really WANT to get wet!
On the rare occasion when they get REALLY dirty (like when Dave walked Kodi in wet grass, then had him walk home on the red clay road on P.E.I.!!!) I have Dave hand the filthy one directly to me, and they go right into the shower for an undercarriage wash. If it's warm enough, I let them air dry, but I also bring a folding grooming table and a dryer along in case I need it. On short trips, we rarely need the grooming table, but we often go away for 3 weeks at a time, and then, no matter how dirty or clean the sites are, they are just GOING to need full baths at least once while we're gone... sometimes twice.
But I agree, a dirty dog never touches the floor in our RV!