I'm not a dom master, but I do have a Plant/Elec. I don't consider /Elec to be a mistake, but in terms of synergy it may not be the best match with Plant/ - Seeds of Confusion works well with AoE, while /Elec is notable for good ST bashing. My usual approach is SoC, Static Discharge, Roots, Carrion Creepers if they're up, then run in and pummel whatever isn't already dying from the DoT, hopping back out now and then to reapply Roots and Static Discharge. Probably not as quick as, say, Plant/Fire or Plant/Psi, but it does the job.
I'm not sure what you mean by slotting issues - posting your build would help clarify that.
@SPTrashcan
Avatar by Toxic_Shia
Why MA ratings should be changed from stars to "like" or "dislike"
A better algorithm for ordering MA arcs
I've look through the guide list and maybe I missed it but is there a Plant / Electric Assault guide out there yet? Having hit lvl32, do I now realize that I've made a terrible mistake in my secondary selection? Frankly, I'm having some slotting issues with Electric. Thanks for any advice/guidance you dom masters can provide.