Not arguing the point. I'm just noticing some issues:
6X 550 in 2S3P for 12V, 1284Ah?
If so, you're doing them harm. The Rolls manual cautions against charging below 0.05C as it can encourage sulfation.
300W/15V = 20A - well below the minimum 64.2A Rolls recommends.
If you're just storing them, fine, that's more than enough to float them, but I hope you're using temperature compensation.
I'm curious how they're being kept warm. FLoating with 300W of solar isn't going to contribute significantly to their warmth.