Winter Storage Question

I would fully charge them and disconnect a cable from the batteries. AGM's are remarkable for the small loss of charge when stored, even more so in the cold Winter months. The best would be to use a float charge, either from solar or AC source but that is one more potential failure point.

With AGM I would either use the solar (no cover) or full charge and disconnect the battery.
No need to have a cord out to trip over.

The majority of WTFco complaints are directed at an inability to go into boost mode which for maintenance purposes is rather useless anyway.

Few comments I have read complain this converter does not maintain a constant 13.6 volts which just happens to be around right for a stored flooded battery in Utah.

Too low for Pianotuna and too high for me, but just right for you.

Lots of reasonable options, really. Lots of not so reasonable options, too, depending your point of view.

Leaving the RV uncovered and allowing the solar system to do its job would be one decent approach.

Charging the batteries completely, making sure the tops are clear of crud, and disconnecting them for the winter should also work just fine. The self-discharge rate in the cold of a fully charged AGM battery is fairly low; it's parasitic loads in the RVs that really make them run down.

Using the built-in converter and keeping periodic tabs on the water levels etc. is reasonable. This was what I did last year without trouble. (Not a WFCO converter, in my case, but a MangneTek 900 series, as I recall, a simple single-stage ferroresonanat converter).

Using a dedicated float charger or maintainer is also a reasonable option. Likewise, using a small separate solar system is reasonable (and a variant on the first idea).

Plug it in. Check the batteries monthly. Whats so hard about that?

JMO but much of the forum negative commentary about WFCO converters is an exaggeration of the facts ... yes, WFCOs may not be the best choice for those with a serious investment in solar and dual or quad 6 volt battery setups who dry camp all the time and rely completely on this combination but the reality is that there are literally hundreds of thousands of RV owners out there that do just fine with their WFCO converter, myself included. My current Freedom Express has a WFCO 8955, yours is most likely one in this series, and for what I ask of this converter it's maintained the single G27 Interstate battery I have just fine. That battery has just gone through it's 9th season, has always been maintained by the WFCO converter in our previous KZ Spree and is currently maintained by a WFCO converter in our current Freedom Express, and is still not showing any signs of giving up. Yes, your requirements during the season may be more demanding than mine which only occasionally involve dry camping but since you're keeping your rig at home for winter storage I'd just plug the trailer in and let your WFCO do it's job.

You have access to house power then put a battery trickle charger or buy a mini solar panel to trickle charge and clear the snow and ice as required.