Kudos to you and your conversion choice. It sure does look heavy.
I commonly add lead weights to the inside of my armor models to give them extra heft. Not only does this give you extra piece of mind transporting it - but it also gives an extra bit of "reality" to the model if it is handled by you or a judge (gasp).
I typically use lead weights for pine wood racers. Super glue works just fine to affix them to the inside.
Calahan