Several manufacturers are still using the heavier E-series chassis for B+ and C motorhomes, but they won't be called Navion because that is Winnebago's brand name for a C on the Sprinter platform. Some things to look at:
Winnebago's Aspect and Cambria lines, although models under 27 feet have been shifted to newer, lighter chassis.
Phoenix Cruiser (direct sales and custom builds) starting at 21 feet and up to at least 27 feet.
Coachmen Concord line from Forest River.
Coachhouse Platinum series 22 to 28 feet on E-450 platform.
If you are looking for used, there used to be many more models of this (B+) type built on E-450, E-350 and comparable Chevrolet 3500/4500 chassis, but more recently the market has been moving to more economical (but pricier) platforms like the Sprinter, and the slightly lighter Transit, or much lighter and lower cost Ram Promaster to reach a lower price point.
Building to near max weight is an issue for most platforms and manufacturers, you'll find few building 10,000 pound motorhomes on 14,500 GVWR chassis. Coachhouse is one of the few that offers some models with an excess of unused weight capacity.
Tom Test
Itasca Spirit 29B