I believe you have a WFCO 9900 power center in your trailer. You can read the specifications and owner's manual here:
http://wfcoelectronics.com/wp-conten...0-brochure.pdf
A couple of "interesting comments" on the WFCO webpage are:
"WFCO’s automatic three-stage converter handles every charging need for the RV while extending the battery’s life. Well-maintained batteries should never need more than two-stage (Normal and Trickle) charging. Our third stage (Bulk) is provided for the rare times a battery needs extra-power for charging. See wfcoelectronics.com for details."
In the WFCO FAQ section is this Q&A:
How many amps does the converter supply to the battery?
It is based on which model converter you have. The converter will provide only the amount of amps that the battery is asking for. This is based on the condition of the battery. Note that the converter defaults amperage to the RV load first, then what is left over goes to the battery. In other words if you reduce the RV’s electrical load then more amps go to the battery causing it to charge faster.
So, if you have a WFCO 9960, you'll have 60 amps of DC power available. Depending on the furnace, lights, water pump, refrigerator, and other 12 volt loads, you may have anywhere from 0 amps to 60 amps available to charge your batteries. I'd "guess" that you'll have probably 15-45 amps available for charging. That's about right for "four golf cart batteries" when you consider that a "typical golf cart charger" works almost like the WFCO with "boost, normal and trickle" charging rates. Most golf cart battery chargers that operate on 12 volts (most golf carts are 36 or 48 volt systems) usually don't deliver much more than about 20 amps max and most use a "trickle charge' of about 2 amps to "maintain the battery bank".
If you don't use a lot of lighting, run your furnace, etc, you should have more than enough battery charging capability from your WFCO without a need for an "add on" charger. If you do decide to buy an additional charger, be careful on which ones you consider. You'd get better information from a golf cart service center than from an RV dealer.