Sorry for the delay as I just noticed your post now, and also thanks to Bill for the feedback on the US2200 which seem like a good option too with a slightly smaller footprint and height than the Trojans. A couple answers to Kent's questions:
1) Your cost estimates are about right for the arch and panels. We, along with many others on this site went with Riza's arch and had it shipped to Australia. The cost, even after having to pay import duty, customs, Australian GST was still about 25% cheaper than if I had a local Brisbane s/s welder make it for me. More importantly though was the fine job Riza did on it as he has all the curves in the right places compared to what I local welder would have done. We constantly have people stop at our dock and enquire where we had it made.
2) The downside I referred to is moving the engine battery from the internal battery compartment to the engine room and making up a new fibreglass waterproof battery box to sit across the engine and genset bearers against the rear wall of the engine room to the RHS of the Racor fuel filter with a separate set of battery switches. Whilst there are advantages in having a shorter cable run to start the motors, we have always been extremely reluctant to change anything on our boat from the original design as the previous owner had taken such great care of the boat with everything in almost "as new" condition when we got it despite it's age. Such a decision for us is a major issue (as was the decision to put an arch on the boat) to think very carefully about however there would be huge benefits in having 675 amp hours available.
3) I am absolutely no expert in these matters compared to all the other regular contributors on this forum however I did notice from all the discussions that Danny has had his batteries (in the above format) since 2009 and that they are still going strong which could possibly be linked to having over 650 amp hours of storage (on the older 8+1 battery design SM2000) and never needing to run it down much compared to the rest of us with 650 amp hours storage and his solar and wind generator setup. I note you also picked up on this potential benefit of more battery longevity with a potentially higher amp hour storage.
This is very tempting indeed but today I fitted the first 8 Trojan T 105's (we now have 450 amp hours instead of the previous 360) and it is clear that I cannot fit another 4 in there due to the height of the box at the aft end where the last 2 batteries would need to go being only 265mm and the batteries 270mm. We would not want a situation where there is no air circulation room above the batteries. There is however a huge amount of room remaining - in fact enough to put in an additional two spare 12v engine started batteries (which are lower) - but not the required height for the 6v's. Based on this we will now stay with the 450 amp hours in the interim and see how we go.
Island Pearl II, Amel 53 #332