Here is
a van that has had some significant work done in terms of aero-improvements. It should compare to your motor home quite well.
They start with a van, and make it very blocky, then do the aero. It is all done by NASA Dryden Flight Research Center, and they drop from CD=0.89 (blocky) to 0.238 (rounded nose and full boat tail). This is not a practical van for daily driving, but it's neat to look at and get inspiration from. It's ALL the way at the bottom, and it's in French, but you should be able to click on pictures for better quality, and it should be easy enough to understand. You can also download the report (from Dryden in English) where it has all bold writing. You may also notice that the difference between their truncated boat tail and full boat tail realized little to no difference. Don't be discouraged by this, because when you look at the pictures of flow patterns on the full boat tail, you will notice that almost everything past the truncation is detached flow anyway.