From your response above I am assuming you mean taking a paper dart like those of mine above and putting a layer of packing tape over the outside to give them more strength and protect them from the moisture inside the barrel? Would love to see the pics.Am I the only one that is using a combination of paper inside for stiffness and light duct tape or clear packing tape outside for my cones?
Looks like I'll have to dig the camera out.
One other method I've tried is to simply coat the new dart cones with fingernail polish. It gives the cones a water proof coating and adds more strength without making the cone stiff.