This is very puzzling. Are you sure both dipsticks go to the oil sump? Are you sure the book says 7 quarts? If so, you could next time put the required 7 qts and remark the wrong dipstick. Two extra quarts normally would wreak havoc on an engine, but apparently has not for you. Maybe the motorhome has a huge sump. Some engines can take 1/4 to 1/2 qt overfill, so maybe yours has a lot more leeway. If it wasn't foaming wasnt't blowing out the seals at 9 qts, maybe 8 qts would be a good compromise in case both sticks are wrong. Do you have an oil pressure gauge? What kind of readings do you get? Any weird readings when it was overfilled?