Need new RV batteries, need advise.

[TWIH]

Maybe he bought the Ebay marine version for $110 each:
1 x EastPenn Deka 24M7 Marine Master 1000Amp Cranking Power STARTING Battery  (Brand New from EastPenn Deka)
Marine Master batteries are renown for their proven dependability and solid performance. This flooded
battery line offers a complete array of starting, dual purpose, and deep cycle solutions for virtually any
marine need. Even under challenging marine conditions like wave pounding vibration, stubborn engine
starting, heavy house power, auxiliary, and trolling, Marine Master batteries rise to the top in user-friendly, 
marine-tough service, and extended reliability.

Benefits:

• High cranking power for quick engine starts
  
• Flush cover, easy-to-install
  
• Extra reserve capacity for emergencies
  
• Maintenance-free design
  

Specifications:

• Voltage:                    12 Volt
  
• Reserve Capacity:    130
  
• CCA at 0 degrees F: 800
  
• CA at 32 degrees F:  1000
  
• BCI Group size:         24   
  
• Warranty:                    12 months free replacement from manufacturer
  
• Length:                       10.75      inch
  
• Width:                         6.75        inch
  
• Height:                        9.375      inch
  
• Weight:                       45.0        lbs
  

Shallow cycling and regular (weekly) ac charges with his improved converter might be ok. If they are at least the Marine variety, which is better than auto starting only, (but nowhere near the true deep cycle or GC abilities) then he could get several years out of them. 
I still think even a 100w panel on the roof would sure help. Thats a bit small but anything 100 watt or more would be good for in between ac recharges.