Man this board is helpful. Here is a summary of the issues raised and my responses.
Grommets. There seems to be consensus that the wires need to be protected from the sharp edges of the knock-out. Various proposed solutions included grommets, electrical tape, rubber fuel line hose, strain reliefs, and metal romex connectors. For now I've wrapped all the wires and/or knock out edges with many layers of electrical tape - I just couldn't bear one more trip to the hardware store. I'm moving the system in a year and will plan ahead for proper protection as well as "craftsmanship in wiring". I do know what you mean.
Split 2 AWG into to neutral bus bar holes. Seems like this is ok as long as both ends stay secure, but I like the add-on terminal block option. I'm going to get one of those.
Two wires coming out of one breaker. Since I have room for another breaker, I'll just add one.
Wire color. There won't be anyone having to deal with this after me because it's a temporary (1 year) setup, but when I move it to its more permanent home I will make sure that all my hots are red or black, my neutrals are white (or white striped/taped) and my grounds are bare or green.
Big breaker screwed into box. The QO box itself is grounded, but I'll look into that "baby box" as a mounting option.
Battery box. The purpose of the battery box is to keep the batteries warm from the heat of the house but to store them outside of the house for space and safety reasons. I understand that there is little risk of them freezing, but I would like to minimize their capacity loss due to the cold. The floor, walls, and cover of the box are all heavily insulated and there is a vent between the back of the box and the house. I replaced one of those little 1" vent tubes with a bigger 4-6" tube, but the gas is still being drawn into the house. I picked up a 3 Watt DC brushless fan with the intention of sealing the hole between the house, poking that fan through, and running it all the time, but the thing was so loud in this tiny cabin that I'm not going to go that route. Now I am considering placing the fan outside over the 4-6" hole in the box lid and suck the warm air from the house, as well as the battery gases, through the fan to the outside. My understanding is that since this is a brushless fan, I should be OK. Anybody ever blow up trying this? Another thought I had was to put some sort of heat source, like a small light bulb, in the battery box to keep the temperature warm enough so that the air flows in the right direction. I will keep experimenting with this until I get it right then let everyone know what worked. Any ideas are appreciated.
Panel frame. I'm going to take the suggestion of putting diagonal cross braces across the frame for lateral strength, and also cable tie the frame down to some ground anchors. Thanks for the warnings from personal experience on this one.
Summarizing this has been as much for my benefit as anything, so sorry if this post was a little boring. If I missed anything feel free to remind me.
To the person who wants to blog post this installation - go for it - and feel free to include this summary of suggestions and responses.
Thanks to everybody. This board is great.
-Walt