I haven't used blue print paper, but I've done the sun prints. It comes with a
bag, and I'm betting the black bags you mentioned would work fine. I had kids
draw on transparency film to make a negative and then print in the sun as part
of a photography unit. I had another class arrange nature objects on the
transparency film and then slide the print paper under that to print. I just
handed them the paper out of the bag when they were ready. You dunk it into
water to fix it once it's been exposed.