Here's my opinion which you are, of course, free to ignore. If you like the floorplan and the Murphy bed get it. Don't over think the storage issue. Without kids along you already need a lot less stuff. If you carefully select items you bring along focusing on what you actually need and will use you may find that you will require less storage than you think you need. We have a couples camper (FunFinder 210WBS 18' box) and after 7 years of use, we still have empty cabinets.
When you equip your new camper try to get things that take up less space. For example Corelle dishes stack and nest fairly compactly and they can be used in the microwave. Nesting pyrex bowls with snap lids can be used in the microwave, conventional oven, freezer, refrigerator, and they can all be stored in a stock pot. Lots of things are made with collapsible silicon like dishpan, strainer, measuring cups, etc.
Bear in mind that we all tend to take more stuff than actually need. Control that impulse and things will probably work out fine.