They do make a dual battery maintainer.....I know this cause I have one that I never installed. I had been spoiled with getting batteries from my brother(Interstate battery franchise owner) so for 15 years I didn't worry about it. ( truth be told he always gave me the good used batteries including 8D and a half dozen 6 volt unless he had 4D's available.....I wasn't too picky!) Long story short, I just had to pay for the first time for both starting and chassis batteries....I didn't like it!! I always leave the MH plugged in at home but I am also thinking along your lines and finally trying out that maintainer.
Sorry for the long post and rambling on...:)
96 Vogue Prima Vista
The Kid's: Humphrie, the Mini Schnauzer and Georgie,wire haired dachshund.
Rainbow Bridge: Laddie,Scoutie,Katie,Cooper,Kodie,Rubie,Maggie, Cassie, Mollie, Elvis, Potter and Rosie Love You! (40+ years in all)