I think that the purpose of having one or some deep cycle batteries is to get around the standing and waiting. Hopefully the solar panel will keep the storage batteries charged (except during use)and then you have those watts to use for your charger and batteries with inefficiencies included. The number of deep cells to be determined by use. In general, you would still charge at home and then recharge or top off at the field. You have already seen it in action and know that it works, so it comes down to price, and adjusting to number of users.
I don't have experience with the system, but your link shows most of the pieces needed. A generator is a good alternative as noted.
For your own use, you can charge and top off using old 6 cell packs to run the charger. Using 3 or 4 packs in parallel of 6s keeps the draw rate low, and the packs may go another hundred cycles of soft use after retired from flying.