sjandbj,
You are asking some very good questions. I will give you my answers which can always be subject to differing opinions. But they are my humble answers.
1. Larger panels are not necessarily more delicate than the smaller panels. I can't speak for all panels of different brands. But most I have observed would have no problem if mounted properly. You have choices for mounting also. A rail system for a single or multiple panels to mount to can act as a stiffener if needed. In addition to a mounting bracket in each corner, an additional bracket can be mounted mid way along each side to help stiffen the panel frame. Sometimes the roof real estate for lack of a better term dictates how the panels will be mounted. Usually using rails two panels or more will mount on or to them. There are very elaborate rail systems available, but can be costly. Rails can be made from aluminum stock available at some home supply outlets and especially metal supply places. Individual mounting brackets are in plentiful supply if you do not make your own.
2. 6 Volt batteries choice. This is one of those things where there is always a debate and facts get skewed slightly to further the debate of each and there is never a winning argument to be had. I used 6 volt batteries because of availability and in my circles and studies I have made are seemingly more popular. Most of the real serious solar installs I know of use 6 volt batteries. This statement is not to besmirch anyone making the choice to use 12 volt batteries. There is nothing wrong using 12 volt batteries.
Weight for the Fullriver batteries were about the same for the equal amps for each bank. 6 volts 6 batteries 672 amps 390 lbs. 12 volts 3 batteries 645 amps 396 lbs. Length of space 6 volt and 12 volt within 3/4" of each other. 6 volt 7" deeper in depth. 12 volt 4" more in height. The footprint of total space for the 12 volt bank would be about 1/2 that of the 6 volt bank. The point of the battery choice is to get a true deep cycle battery which is not the same battery as a marine rv battery.
My previous rig had 4 6 volt Interstate U2200 golf cart batteries which are commonly known as lead acid or flooded cell batteries. They were five years old and still going strong when I traded them in as cores for the AGMs. So I had good service from 6 volt batteries and had no problem using them again. As stated previously my AGMs came from Discount Solar in Quartzsite AZ. During the season they sold hundreds of the DC224-6s and they were their most popular seller.
I am not trying to make a case that 6 volt batteries are the best or only way to go. I am simply stating my case why I used them.
3. Regarding the auto disconnect for the converter you speak of, I am not familiar with it. Actually I am not sure you would need to spend the money on one. What I have found is the solar in the past has always kept my batteries charged and the converter is not needed. My previous rig had the converter unplugged and not even hooked up to the batteries. I doubt I will need to use the converter. I could use a 15 amp outlet to power the converter independently from the coach and at the same time use the inverter to power the coach circuits. Or use the Honda to run the converter while using the inverter for coach power. I moved the converter to the front bay to simplify plugging it in if I wanted to. I made up a short extension cord with a 20 amp female plug end to hook to the converter because the converter has a 20amp male pigtail. I think most people just unplug the converter and forget about it when they have a functioning solar system.
Steve it is good you are doing your homework researching solar panels and probably other solar systems requirements. There are many sites out there that are very helpful. Several folks here on the forum have systems that serve them well and are well installed. Most all are probably different from the next one. The goal is to have an efficiently well working system. If you have not visited Jack Mayer's site, I would recommend doing so. Jack has a information packed site. Not so many photos.
I wish you the best with your solar project. Joe