I don't think this got mentioned but another way to save up... is to start a few quick trap upgrades (e.g. seeking air bomb, or lev6 small bomb) about 1 day (for seeking air) or 2 days (for small bombs) before the TH is done... and then cancel after TH upgrade is done.
E.g.
Lev6 small bomb costs 1.5 mil each... if you start 3x, then you spent 4.5 mil. You have 2 days to make that back through raiding. Then, once TH is done, cancel all 3x and you get 2.25 mil back. It's crazy to lose 2.25 mil but it's one way to start 2x infernos right away.

