Can it be done long term?

I planted 50 Thujas (emerald green arborvitaes) along both of the back yard my property lines a couple years ago in the hopes of growing a privacy fence. They did great until last winter when most of them on one side died for no apparent reason :-(. I think maybe I smothered the roots with too much mulch or possibly the neighbor sprayed round up along the fence-line on a windy day (?)

Anyway, I dug up the few (8) that survived, and put them in temporary pots that blow over constantly. Now I am wondering if I could put them in big heavy pots somewhat permanently and use the dolly to move them as a sort of portable screen. I have seen 7 foot tall ones in pots at Home Depot so I am sure it can be done but what do I need to know? Should I use gritty mix or 5:1:1? How often would they need root pruning/re-potting? Would they need winter protection in zone 7?

Thanks!

Nik