A single group 27 battery about 100 ah, is plenty for LED lights. That’s 50 ah usable, or 600 wh. That would not be a hard install.
If you start to turn a fan on, either ceiling, stove or restroom, that draws a bit more power than the LEDs. Add on a TV and a couple other not too much. Things, and a second G27 battery may be needed.
So, as long as LEDs are all you power, and you shut them off when not used, you should be fine.
I only know my RV< and I think a 55 amp charger is way too much for a single group 27 battery, that would be a perfect size for my 4 golf cart batteries that are 458 ah. My OEM converter that came with the trailer, don’t know the rating, but it pushes 15 amps charging until voltage reaches 13.6, then it tapers down the amperage.