Bare minimum would be 10,800 per day. I'd advise keeping more on hand in case someone decides to come knocking with a mortar.
@ Dr Who
No, your base should not have went from 86% to 0% in 15 minutes, even with no repair materials and no crew. However, someone could have easily helped it on its way to a low percentage in the time frame you've given. Doesn't make sense that they wouldn't have finished it off though.
Yeah, I suppose the only possibility without it being some glitch is that someone pew'd it down to 1-3% and then logged out before he could get pinned with it.
And again need in seeing what happend to your base. I hope we get some of this. because people will just brake their head with thoughts of what happend. make a sort of black-box or something. so base could show who were near it in last 12 hours so you could be 100% sure who did this to your base