I've made several cheesecloth ghosts (static prop only, though) that were real attention getters. They were made out of a blucky skeleton (just the torso) and draped with cheesecloth. The arms were extended with 2 wires (coat hangers actually) routed from the top of the head down and through the arms to keep it stiff. Any cloth soaked in RIT whitener should react somewhat under a blacklight. Not too sure how it might look for a colored cloth, but my brownish skull was still UV reactive after soaking in a RIT bath.
In theater crowds we mix 20/80 glue/water & use it to wrap semipermanent styrofoam pieces before painting. it helps keep the foam from tearing out & getting dingedup. It also profides a nice base texture. I've done toomstones, stone walls, brick walls, rocks, & trees this way.
The props have held up for multiple shows including nearly nightly setup & take down.
I've tried a number of methods and materials for optimum brightness under UV lighting. Cheese Cloth soaked in Fabric Whitener and tumble dryed seems to work best. For color, Nothing is brighter then plain white. Colored CC simply doesn't "pop" - it has a dullness to it.
RIT whitener works well, but my experiance is that a product by Dylon called "Double Duty Whitener and Stain remover" produces the best results.
Try a fabric store like Joann's, they usually have some on a bolt that can be cut to length.
Soaking cheesecloth (or sheets) in liquid laundry starch and then draping it over a form (I use 2 liters, milk jugs, whatever is handy to give it shape) to make ghosts. When it drys you can place them wherever or hang them.