One thing I seem to see more and more are people who are at a slip and use solar to charge batteries and keep refrigerator cold so they don't have to plug into the normally pretty dirty power of a marina. Gives a nice flexibility as to where to get a slip too if you don't need power. If you are building a system make it as flexible and give you the most self sufficient system you can.As I get more into this, it seems like I will need to build a bigger bank with at least another Group 27 or go all the way to a Series/Paralleled bank of 4 T105's or equivalent.
Your comments and research on the charge controllers is fascinating; I hadn't really even thought about which controller I might use and this bears some further study.
How will I use the boat? Well, for the spring and summer, I'll be on shore power when I'm in the slip and the inverter will be off and Engle running from 110. I'll probably make a few weekend trips with whatever setup I have and make some measurements on how feasible it is to run from the second battery bank.
I have a primary house/starting bank of two Group 24's right now that are charged from an on-board charger and get a trickle from the tiny 35A on my Atomic 4. I don't plan on having any connection between this bank and whatever other bank I install as far as use or charging from the engine - but I may consider using one of my 3 legs on my 20A, 36V charger to top off the secondary bank when I'm on shore power.
Next September (God and finances allowing) I'm hoping to embark on the Great Loop and will be living aboard for up to a year. When I drop the mast and head over to Chicago, I'll be in for 1200 miles of motoring and will keep bank 1 topped of with the engine and occasional shore power charging. Using the Engel as either a freezer or refrigerator draws the same 2.75 amps on a (guessing here) 30% duty cycle and with minor use of the inverter as noted previously, think that this combination should do the job.
I really appreciate everyone's inputs. Like many other things in boating, adding solar and making equipment and use plans entails lots of research and decisions. I am grateful for the collective wisdom of the group.