Default Need Nandroid Backup Help!

I have a US Cellular Galaxy Mega I am going to follow the instructions on here for rooting the device. The problem I am having is I want to use TWRP for the recovery and I have been told I need to use the one in the thread first then root then replace it with twrp. My issue is I want to make a Stock Unrooted TWRP backup before I root so I can have it as a fallback. Can I just use TWRP for the root process that way I can make a Stock backup with twrp or am I stuck using philz??