I looked into using an 803a to automatically charge a solar battery bank as a way to run off grid without burning so much fuel. The problem is a diesel generator should be most efficient around 80-100% load (as I understand it) and even loading an 803a to full for charging would take a MONSTER Solar battery charger/inverter.
I'm curious why your using an 805b for off-grid, are you running a large shop with it?
Also to actually answer your question augmenting it with solar will work in 2 ways that I know of.
1. A solar system is meant to augment "mainline power" so if you hook your generator to the solar system like its main power the solar should reduce the load on the generator. In this case the generator would have to run 24/7 because once power is lost the solar system shuts down. (to prevent backfeeding the grid)
2. You can hook the generator up as a battery charger and use it exactly like you mentioned in post #4. As mentioned earlier it should be possible to setup an auto-start system tied to the battery state of charge via the Solar battery charger/inverter.
For this you would have to do some digging to see what Solar battery charger/inverter would support this out of the box.
The original post said he is off grid, so it is not a grid intertie type system, and he is relying entirely on solar/gen power.
That being said, I have several customers that are off grid and have solar and/or generator systems.
Even the ones without solar only have to run a generator 2-3 hours per day, and the ones with solar might go for several weeks in excellent weather without running a generator.
They adjust their lifestyle so that the battery bank operates the low draw equipment, such as lights and entertainment, but when it's time for heavy loads, the generator runs. By that I mean things like the well pump, as all the major appliances that can be are run on propane (hot water, furnace/hydronic floor heat, laundry dryer).
Water supply goes from well to 1000 gallon or larger water tank, then a lower powered boost pump for pressure to the house.
Then again, I also have customers that use all electrical appliances, and just have an oversized battery bank and inverter to deal with the demand.