Using Wrathful Skies w/ National Troops

[Thufir]

I've done some searching, and it appears (to my surprise) that both Thunder Ward and Storm Warriors provide only 50% SR. Does this mean that it is impractical to use Wrathful Skies in combat where there are substantial numbers of troops without natural lightning resistance?

It is possible, I suppose to cast both TW and SW (I would guess they stack), but that sounds expensive, in terms of gems, fatigue and casting rounds. Or perhaps w/ only SW or TW, do normal troops Last long enough w/ 50% res to make it worthwhile? Does anyone out there have experience using Wrathful Skies w/ normal troops and any combination of these spells?

TIA,

Thufir