Outside of convincing you that the building attic is a poor choice, the only solution I have is a cooling rack.
The Powerware 9390 – 120kVA should remain between 68 and 77 degrees with a limit of 104 before issues arise (according to the manual). The racking you choose should take into consideration the rate at which heat will be created by the battery.
I hesitate to offer a racking solution because I do not specialize in them. I do know that they are typically designed to fit the environment they are in. You may be able to co-locate this with a ventilation system to reduce the amount of cooling required.