well the pieces i use are foam surrounded with card, hense foam board, what i have done in the silencer is to minimalise the area that is left open, on the edges of the laser housing i have covered them with a thin layer of modeling putty so it has set hard, the other parts are covered with multiple layers of paint, enamel and varnish to give it a scratch resistant covering. any large areas which are left open will be covered with some rubber paint i have which provides a waterproof layer when moulding. all in all i won't mould the items until they are sealed, the silencer should be fine now as it only has to stand up to molten rubber gel stuff for a few minutes until it cools, should be able to withstand it.
and i will be making a cast for myself, most likely the first version which will be sanded, cut etc to get it accurate, then the previous moulds can be melted down and remade into the new ones. when this is ready i will be adding them onto the classified area so if your interested pm me now and i will inform you when they are done, otherwise watch this thread. i will be hoping to make about 5-10 casts depending on who want them, uk only at the moment, kit forms for worldwide.
also i have tried looking st the uk alternatives but most are still very expensive, i tried latex, my advice to others, don't even look at it, it shrinks to much, its too flimsey, i had an AR and tried to mould it, made a plaster cast around it and guess what, it failed, the cast is now in my cellar along with other artifacts of my tortured past... silicon is too expensive and needs vacuuming, this stuff i found seems to be my best chance as its cheaper than the silicon and can be reused, just is not as durable as silicon so will need to be remade every few casts.