Glad you're back! As far as I know, a water/fuel separator is mostly for diesels. Can it be used for a gasser (your 454?) I don't know.
As far as correct oil...if the dipstick says 10-30...use 10-30. I would suggest...due to the age (30 years) of the motor to keep using fossil, altho the more expensive syn would do fine. Don't forget the filter (any name brand will do) and grease the chassis. Keep a schedule (every 3-4000 miles or twice a year) but the bottom line is to USE the motorhome. Letting it sit for months at a time does more damage than anything else.
