I don't know if you guys ever thought of this but, with the tnt only affecting faction land while the faction members are online, if I was getting raided, I would just log out right when they light there tnt cannon so it has no effect, then get back on fight more and repeat. Now the first question will be "DUHDUH YOU USE XWAY TO SEE THE TNT CANNON DUH" no.... just get on top of your base it is easy. So maybe this was never thought of but it is just an idea, thanks.
(BTW I have a sky base so I would not be vulnerable if I got on top of it, for others i would suggest a small room up top where you can shoot arrows from and see out of.)