Check the electrical design on your trailer. I have a 2010 Starcraft 246RKS. This 28' trailer had the batteries on the front tounge and converter in the back connected via 8 guage wire. A little research (mostly @ http://wind-sun.com/ForumVB/index.php
showed that you really can't expect to charge your batteries over that much wire - especially with that guage.
Maybe if the factory had run 0 guage I could have gotten a near charge, but still not good. After a bit of thinking and learning on the net I decided to move my converter to the front storage compartment - so now it is less that 6' of 4 guage cable from the batteries. In addition I replaced the 8 guage with 6 guage to go to the power distribution (which I left in the rear). In addition to the run of 6 guage, it required running new 110V cable from the old to new location.
After that, the charger actually can recharge the batteries fully, but the other thing I learned is that the low end Iota converter provided in these trailers is essentially a 2 stage trickle charger, putting out 13.6V in the charge phase. A bit of research later I realized that it might take 12 hours of generator time to recharge a nights use of the furnace. To solve this, I replaced it with a Progressive Dynamics unit
There is some debate on to which is better between higher end Iota's and this unit, but I had one of these in my Casita and it worked great so I went this way. In addition to it's 14.4V full charge - it has a cycle every 23 or so hours that is supposed to prevent stratification in the batteries. I think it works as I believe my Casita battery was the original and the trailer was 7 years old when i sold it.
Main point of this post is that RV manufacutures don't always build their trailers to be effective boondockers. The most important changes I made, moving the converter and increasing the guage of wire from the converter to the batteries, cost me around $100 and 8 or so hours of my life. Had it been done at the factory I'd estimate their increased cost at way under $50.
I bought this trailer used and learned that the prior owners 1) rarely used the trailer and 2) didn't leave it plugged in. That in combination with the fact that with the factory installation of the converter the batteries could NEVER actually be fully charged, leads me to believe I need to replace them. Next steps will be:
1) buy a hydrometer as that seems to be the only REAL way to test your batteries and they are cheap
2) replace them. I think will be be replacing with 2x Trojan 12V true deep cycle batteries. something like the T-1260 12V deep cycle.
I know many use the 2x 6V and while I think those may last longer - as a weekender my batteries won't go through huge numbers of discharge/charge cycles - and with these I will get more amp hours available than say 2x T105's.
I know this is a bit technical, and I'm not much of a writer, so feel free to ask for clarifications