To make the Pouldren for my Phase 2 Rex I used
*1 Blue ARC trooper pouldren
*1 CW fordo pouldren.
First, I had to cut the Ammo Pouch of the Blue ARC troopers pouldren. I then had to cut the pouldren so that the big bit was only on 1 side. I then restuck the ammo pouches back onto the pouldren using Blue tack to keep the pouches fairly stable while I squirted some glue on it to reinforce the blue tack. Then I cut the back part of Fordo's pouldren off and stuck it on the back of the Pouldren, the same way I did the ammo pouches. I then painted the whole thing black, then after the paint dried, I painted some bit's in Adeptus Battlegrey and painted the big end of the Pouldren Mordian Blue.
I hope this has been useful.