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Back to the question about how much panel Wattage for a 200 Ah LiFePO4 battery. 400W is on the low side from my experience, but is just fine if it does the job you want done. I have 800 W per 200 Ah battery and could have used more a couple of times (almost had to run my generator!). How much solar you want depends on 1) your nightly load; 2) where and when you camp; 3) battery size; 4) how long you camp; 5) whether the panels are on the roof or ground; and 6) how adverse you are to getting the generator out to charge the battery during less ideal sun conditions.
The following is based on roof-mounted . . . . ..
There are places and times where 200W would do the job even with 75 Ah of after-sunset energy draw from the battery. And there are places and times where my 800W isn't enough (e.g., the California central and north coasts in fall and spring and about 90 Ah of use). By "do the job" I'm talking about very rarely needing to fire up the generator.
So, the smart thing is to allow for expansion of the solar. Rarely needing to run the generator is addicting and your energy usage may drift up over time.
Allowing for expansion mostly means use a roof panel layout that allows for more panels in the future. ((I didn't do this and have had to move panels twice and finally remove some panels and replace with larger panels))..
It's always possible to pull additional wire and add a second or third solar controller so those are not so important. But, moving panels to expand the array is a bit painful.
Beyond the above, an option is to "over panel" the solar controller. The solar controller will have a "maximim" solar rating that is above and possibly well above the nominal rating. Solar controllers simply raise input voltage to limit power when the solar produces more than the controller can accommodate. At one time I had 40% more panel wattage than the controller could make use of. This sounds wasteful, but most of the time, particularly in fall/winter/spring and summer morning and afternoon I was not maxing out the controller and so was getting 40% more energy than I would with 100% panel wattage. Of course, for an hour or two per day around noon on very sunny days in the summer, the solar controller was maxed out and I was "wasting" solar. However, unless one is running A/C during those hours, this "clipped" power isn't needed and won't be noticed. That said, over paneling by 20% is more typical (and where I am today). Home solar systems are usually over paneled by 20%. With 20% one only loses about 4% of the annual energy production, and that occurs on clear sunny late June days when the production is well above requirements.
For example, my sub-$200 Epever 40A controllers have a rated charge power of 520W but a "max PV array power" of 1500W. Max voltage is 138V at 25C. I currently have 600W on them.
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