TracyCess,
If you've had those batteries on the charger for 3+ days and they are only showing 12.3V, then they are not properly recharging. Wahoonc makes a great point that you should have a shop test them, but it sure sounds to me like they are shot. If your portable charger has an equalize or desulfation mode, try that too.
You are correct that when you are running on shore power, your WFCO converter should be running at 13.6V and that is what you should see at your battery posts. As wahoonc says, it sounds like your converter is not operating. Before deciding that the converter is toast, you should check that you are actually getting power to it. My Aspen Trail did not have a dedicated A/C breaker for the converter; however, it was tied into the breaker labeled "GFI". So check your A/C breakers and make sure they are all switched to ON. Depending on how far you want to dig into things, you can remove the cover of your A/C panel and confirm the wiring or see if something has shaken loose and disconnected. But heck, I personally would jump on the legitimate reason to upgrade my WFCO so maybe just do that!
Since you primarily boondock and don't use a generator or solar, how do you recharge your batteries while out camping? I ask because if you hook up the trailer plug and run your vehicle for charging, this really provides very little charging current and it would literally take days to bring a low battery back up to charged. If this is what has been happening, it has been really hard on your batteries and is likely the culprit behind their short lifespan. Well that on top of a non-functioning converter! The rule of thumb is to not run you batteries below 50% charge (roughly 12.0-12.2V), although true deep cell batteries like your 6V are designed to deal with deep discharges. Ideally you would have a way to quickly bring them back up to 90%+ charge (~12.6V+). Batteries can relatively quickly and easily get back up to 90% charge; however, it takes a lot more work (time) to get them all the way to 100%. You could conceivably run a generator for a few hours and your converter could recharge them back up to around 90%. The charge voltage has a big impact on how quickly they recharge. This is where my discussion of a 14.4V bulk charge rate comes in. The 13.6V of a WFCO works fine if you were plugged into shore power for days, but if you've only got a few hours for recharging then you want to be charging at more like 14.4V (or even 14.8V for a pair 6V in series, as recommended by Trojan). Once you get back home, plug into shore power for a couple days to get the batteries topped off to 100% (~12.7V+).
That was a long winded way to say I concur with getting some solar! I love ours. While I do have a generator, I almost never use it. Only if we want to run the microwave or air conditioner. Solar is not a quick recharge; however, it is charging every day all day when the sun is shining and your batteries will love it. Also keeps them bursting full during storage if you're stored outside uncovered.
