Just upgraded to dual batteries on our new 19H. Used the existing battery tray, bent the sides flat and built a subframe out of 1 1/2" angle aluminum, riveting each corner together. Wired in parallel of course and works great. Let me know if you'd like additional pictures of the frame, would be happy to share...
Great forum, look forward to sharing and learning!
2011 Jayco Jayfeather X19H
2005 Toyota 4Runner V6
Blue Ox Sway Pro