How can I correctly create and apply armor/packages to Rthro efficiently?

I was just wonder what the most efficient and most professional way of creating Rthro armor/custom packages. I have attempted creating some in blender and when I exported it into roblox everything becomes misplaced and so forth. If you have any clue on how I can do this most effectively that would be greatly appreciated. PS this is the rthro rig I base off of " https://gyazo.com/f5ad508c8ffcb197c4cf7c66da0af864 "