Sintra is just a big flat PVC pipe. Same material. I cut the shape I needed, first using newspaper to create a stencil. Then I made a big pot of boiling water and dipped it in for a few seconds. I was able to shape it with my bare hands. Now, I don't think you could get any raised box-like areas that you'd have on vacuformed TIE armor, but you'll be able to bend it at the sides and the should strap areas.
Scott