An update from here on progress after being out a few days and why setting up a system is not that straightforward. Once commissioned then yes, simple.
These batteries are outstanding. Sucking up every bit of power thrown at them. None of this watching tail current decaying slowly from 80% full.
In normal use, these batteries are going to be simpler to look after than LA's. We use 100Ahrs overnight (typical) and the last few days the solar has put an additional 50Ahrs back in per day. With 300 useable Ahrs in the 480Ahr bank (maybe more), that means you can go 5 days without running the engine. In the summer with a bit more sun then we will never need to run the engine. No need to fully charge. Once you get into a cruising routine, then maybe once every 6-8 weeks think about taking them up to 100% to synchronise the amp hour counter......and not think about them otherwise. This fits in well with Peter's....it is simple. It really is.....
BUT.
Initially, there is the 'not so simple' construction of a system to prevent overcharging and over -voltage. The 3 peeps on here have all got slightly different DIY systems and mine is different again. Anyone thinking about going the LiFePo4 route needs to pay attention to the differences. The snag I am coming up against is that I had hoped to terminate charging from the various charging devices by voltage alone. Peter does his by voltage but he is ONLY using Solar so easy to control that source. T&B charge normally via the alternator and that backs off when it reaches a voltage and tail current (via an Arduino device) and MP has an Arduino device that disconnects all his charge devices based on voltage AND tail current.
In practice, the voltage target to get to 85% SoC increases with increasing charge current, so I would need to terminate charge at say 14.0V if charging with our alternator on a 45A setting, at say 13.8V for charging via an IP22 at 30A and maybe 13.6-13.7V if the solar is only putting out 10-20A. MP has been trying to tell me this for weeks. Its only now the message has been understood having played with it for 2 weeks.
I have found that tail current drops rapidly over 30 mins or so once SoC gets over 95%. Up to 95% the charge current is rock solid. No reduction at all. If you have a controller that can measure and use the current measurement, then termination is easy. Problem is that you need some sort of 'brain' (ie an Arduino) to monitor voltage and current. Unfortunately the BMV 712 measures tail current but current is not one of the options you can set off alarms or the relay. The Arduino seems a very good solution.
I will try and see if I can find a compromise based on voltage with maybe choosing 13.8V as the terminating voltage and accepting that if charging over 50A I will only get to 70% SoC (but that is fine anyway). The only issue I see then is if I have a day of 4-5hours motoring and getting up 90% (so it doesnt terminate) and then getting lots of solar late in the afternoon. I am not sure if the backstop of the cell monitoring BMS box that disconnects at 3.8V would ever be triggered.
With the Sterling AtoB attached to the alternator I have 4 battery type settings that vary not only the absorption voltage but the current. The two gel settings give me 45A and 55A so I have a number of various permutations. I need a few days of good sunshine to test the high voltage disconnect.
One other problem I found was my two solar controllers fighting with each other. Sorted that by just using the 30A mppt for all the panels (total 500W).
Peter's 'solar only' is a very simple system with no dramas at all. Once I understand the top end disconnection, mine will be very simple as well.