We have a 1999 Jayco on a Ford E250, 19.5' plus rear mounted spare. Ours has the jackknife couches that make into a full width bed (storage underneath), single electric burner, compressor frig, sink with small freshwater tank, TV above cab (removed and made more storage space), microwave, roof AC and 2800 generator under the back. It had a really disgusting recycling toilet all the way in the rear on the side where if you were more than 5' tall and 120 pounds you would have trouble using. I tore it out patched the floor and put a cabinet in it's place for general camp stuff (leveling blocks, hoses, power cords, tools, etc). Ours had a removable extra bucket seat inside the side door, I removed it completely including base and fixed the floor and added another cabinet there for more kitchen storage and extra counter space. Built a wooden box that is upholstered that clamps down between the buckets that our new porta-poty slides into. I also added a swivel base to the passenger seat, you have to move the porta-poty box out of the way to swivel (then back in place) so we only use it when we are going to be somewhere more than overnight.
I was able to find some online manuals for mine but they didn't really help much, pretty much told you what you could figure out spending 5 minutes in the van.
I think there is at least one more Jayco owner on the list. Welcome to the very small owners club.