Title says plugged in and body says plugged in at 100%; these can be separate concepts if one has fine control over the charging voltage.

Will leaving my things plugged in at 100% hurt it more than constantly unplugging at 80% and replugging at 20%?

Plenty of academic research out there showing that pegging Li to 100% SoC reduces cycle counts to EOL (by electrolyte degradation and other processes), especially at higher voltages/temps. You didn't mention capacity reduction associated with charging at freezing temps so I assume that is a non-issue in your use case.

It seems to me that if leaving it plugged in is an option you have shore/mains/grid power. So I'd

• charge to middling SoC and unplug the powerstation (according to the manual); and
• run the loads off the wall socket

Am I missing something here?

offgrid with LiFePO4

I live offgrid with Li on a very limited budget, so performance and maximal cycle life is a practical matter for me. Based on my own reading and experimentation I charge my 4S LiFePO4 to 13.8v (3.45Vpc) until Absorption falls to 0.10C then quasi-float at 13.31v (3.3275Vpc). I warm them to 50F and charge at ≤0.4C.