DC/DC step down and SPDs for Midnite Solar E-Panel?

Hi,
I have a few questions:
1)  I have a 48v, 225 amp hr battery bank (Eight-  6 volt batteries).  I want to step down directly off the battery bank  to 12 volts, then go to a breaker panel where I  have my 12 volt lights going into.  Can you recommend a DC/DC step down transformer that will handle my 48v 225 amp hr battery bank and allow me wire as described?

2)  I have a Midnite Solar E-panel.  I want to install a SPD in the E-Panel .  I see that Midnite solar has their version of a SPD.  Can I put a Type 1 or Type 2 surge arrester in the E-Panel i.e Square D HEPD80 or something similar instead of going with the Midnite Solar SPD?  I want something with a response time < 1 nanosec.  Midnite Solar's response time is <15 nanosecs instead of , < 1 nanosec.

Thanks!!