I have heard unsubstantiated rumors that there may be warranty issues between GM and Jayco regarding the lengthening of the chassis for the Seneca. Something worth looking into.
You might also look at the Greyhawk built on the same chassis, but with a shorter wheelbase. I have not personally driven the Kodiak chassis but read that it is a dream to drive.
Good luck in your hunting,
If interested, come visit us in the iRV2 Chatters chat room. We're there just about every evening from about 8:30pm eastern until about 10:00pm. It's a great bunch of folks!