Suggest you look at the line of Iota chargers. Check out the chatter on this Board, the SSCA board, and the Cruisers Net board. Great chargers. Modestly priced. Hi-tech multi-stage PWM charging. Robust. I have two.
You can find them on eBay or at Jackrabbit Marine, among others.
For your total 300AH battery bank, you need a charger of at least 45A capacity. The Iota DLS-45 or DLS-55 would be ideal. If you get one, be sure it has either the internal or the external IQ-4 smart-charge device. They come both ways.
(I have no connection to Iota....just love their chargers)