[A/S] Water Heater Question

[SHMossLanding@xxxxxxx]

We have a 1965 Overlander, andneed to replace the water heater.  My question 
is, the current plate isays it is a 9 gal.  Will I be content with a 6 gal 
Atwood, or should I go with a 10 gal.  I have read it is more difficult to 
install a 10 gal rather than a 6 gal. We used the unit for weekend travel, 
and usually just the two of us.  I never had a travel trailer before so I 
would like to only replace the item once. Any help appreciated.
                         Chuck & Lynn
                         1965 Overlander