Connecting Solar Charge Controller output to RV system

I doubt that there would be any problem with doing that.

There are two main reasons for keeping the cables as short as possible to the battery. One, as you indicated, is to minimize power losses. The other is to give the controller as accurate a voltage reading on the battery as possible so that it can determine its state of charge.

Given that the WFCO is already handling that for your RV, I'd imagine that the existing cabling losses are not significant. Therefore, it shouldn't be for the Renogy controller either.

And the controller's job is to take care of the battery, no matter how many there are. Both should "coordinate operations" between themselves based on the battery voltage to assure that the battery isn't overcharged by either one.

Just an additional note, I have 4 chargers, the WF8900 (55amp), as you do, a MPPT 40 for solar, a Xantrex TrueCharge 2 (40a), a pair in parallel, there is no problem with mine dealing with each other. I do use a TriMetric Monitor to keep a close eye on all the charging, it is also an awesome piece of equipment. The TrueCharge 2, gives me the option of equalizing the batteries at the manufactures recommended output, for my batteries that is 15.3 for two hours. If you boondock a lot, this would be a exceptional monitor, to work with your solar system.

Andrew, what kind of batteries are you using? You might be a bit heavy with the 40a charger unless you are working with at least 220+AH. The controllers/chargers should all be charging at the correct rate together, as provided by the manufacture of the battery. They will not work together if your settings are way off from one controller to the other. The system will see the most powerful one and the others will probably shut down if they are automatic thinking they have come to full charge. All mush have a capability of over voltage shutdown and under voltage shut down. However, why are you using a three phase controller? Is it programable? I know nothing about this controller. What is this system being used for? If it's three phase it is not an RV so must be in a commercial zone? I should say that I replaced my MPPT 40 with a 30 as the monitor for it is integrated together not a stand a lone monitor. It sees all my controllers which are all fairly close to the battery manufacture suggested settings. So I have one working when I'm disconnected from shore power, one when connected and the Truecharge2 primarily for Equalizing my battery at the correct voltage, which was impossible by using my previous chargers/controllers.