DRAFT
“It is cheaper and easier to use less power than it is to make more power.” – highdesertranger
…the why is important. If you are trying to meet a specific performance goal you can save money by identifying performance bottlenecks and upgrading the relevant components. If you want to do the upgrades because they sound like a fun project then throw all the parts at it you want with my sincere blessing. I certainly am not immune to fun projects. – secessus1)
So your existing power setup isn't meeting needs and you want to change it. Maybe your daily power requirements have increased, you bought a pre-built van, or your use case has changed.
* if your existing system usually meets needs but sometimes falls short in anomalous circumstances * if your existing system is close to meeting needs (like within 10% of hitting [your daily power requirements](https://rvwiki.mousetrap.net/doku.php?id=electrical:12v:dailypowerrequirements)) then for several reasons a LiFePO4 swap has a good chance of closing that gap with no other changes needed. * if your existing system is far from meeting needs then other upgrades would be required. Solar, as you say, and/or replacing any existing relay/isolator with an actual DC-DC.
There is a saying that
defining the real problem is is 90% of the solution
… and that applies here. I understand why we humans don't want to spend time/effort figuring out the problem. It's not fun and we don't get to buy stuff yet.
There are two main areas where the problem can reside, or it can be in both.
This is listed first because reducing demand is free2) and trivial to test. It's like the old joke:
Patient - “it hurts when I do this (sticks finger in eye)”
Doctor - “Stop doing that.”
Some loads are mandatory and we can't “stop doing that”. Your insulin might require a powered fridge at all time. But many high-current loads newbies try to run (and crash their power setup) are easy and cheap using traditional methods. Electric water heating vs propane water heater (or kettle over a stove), for example.
Sometimes just changing when the load runs can eliminate/reduce required upgrades. Consider a system with limited Ah capacity that sags under load and trips the inverter's low voltage protection. Running that same load when the solar or alternator are making power can reduce the sage, reducing or eliminating the problem.
Supply problems can the broken down into charging, bank capacity, and throughput bottlenecks.