PVC mannequin - front view

2.5" dia. PVC is used in conjunction with the black (sewer-type) Y-joints at hips and feet. The joint at the left knee was going to be used for a bent knee pose, but it was too unstable, so a straight coupler was used to replace it.
Joints used:
R arm: 45°,45°
L arm: 90°, 45°
Neck/shoulders: 'x' piece
Pelvis: 'x' piece
Hips: 45° Y joints
Feet/ankles: 45° Y joints

PVC mannequin - side view

Tip: prime and glue all joints EXCEPT for the shoulders and forearms - that way, you can pose the arms as desired.

Poseable hand detail

wood 'palm' with 2-inch long 'wrist' (goes inside PVC), coathanger wire, wood screws with washers, and 1/2" dia. tubing

Wig head

A wig head is used so that the helmet sits correctly on mannequin (no 'bobble-head' effect).
Using a piece of PVC and coring out the wig head for size would have been much easier than making the dowel and block!

To get the proper form for your armor, use some padding around the torso and thighs.
A thick foam camping mat and plenty of duct tape works well (strap it down hard where it should be more narrow). When fit with a second pair of gloves (cheap batting gloves are perfect) and some cheap black pants and shirt, it's super easy to remove/replace the armor as needed, and just leave the 'soft parts' in place.