We just completed a 6 week 6800 mile trip in our B+, a Leisure Unity MB model. We always use the coach shower. The only limit when dry camping is the 30 gal water tank. Holding tanks do just fine. We also travel with a cat. The key is compatibility with your spouse and each understanding that everything must be kept in it's place. This took a little practice on our part as we downsized from a 36ft class A coach. We do tow a small car and did have to pack a few winter coats etc in the car. It seems we always take too much, but you need your STUFF!!
We are towing a new Chevy Sonic. The Mercedes has no problem with this 2700# car going over 11,000ft passes in Colorado. We consistently averaged 16.3mpg.