Looks like you're really coming along there bud!
Do the resin in a warm, yet well aired place, wear a face mask if you can, I suggest you coat once, then do a second coat straight on top as you may have dips and troughs in the armour where the resin won't pool as deeply, so when you come to sand you won't find you're sanding back to the cardboard.
If you want a thicker mixture try adding a filler powder like french chalk (talc) or even bondo (Which makes rondo). Rondo is probably better as it will sand back easier for you.
If you wanted to be REALLY clever, you could wax your cardboard bits, put a layer of fiberglass over the top and then use the resin as a gelcoat. The wax will prevent the fiberglass from sticking to the card and you've just made a fiberglass copy of your armour 
Neat eh?
