I don’t k ow for sure as I don’t have this model coach. However, generally they do have two filters (one is a water separator) and they are usually right next to each other. Fuel/water separator would be closest to the tank (first in line), and have a drain on the bottom of it. They’ll be close to the same physical size as well.
You may also have an algae issue. Black sludge in the tank. Did you happen to dump out the jelly from the filter you changed? How did it look? How old is your fuel and have you been through a bit of it recently?
I looked at the brochure and it shows a service area that’s supposed to house the filters and it appears to be along the frame rail, so you’re looking in the right spot.
2007 HR Scepter 40 PDQ
400 ISL, ~67K on the clock....for now