Hello,
I am having trouble joining this object into one closed polysurface. One open surface has non-manifold edges and I can’t seem to close them. can someone help?
Steven, your example didn’t come with your post. Try again. —Mark
I have just posted it on this thread
hi Steven, thats a wild boolean mass as you call it yourself in the file 
if you click on the big part and hide the rest you can use Invert and Hide for this then use ShowEdges and select Non Manifold Edges - one edge shows up. if you explode it and hide the surface covering or involving that edge you see that 3 surfaces are being joined at one edge which so called non manifold. you have to find a way that obliges your creativity of course not to let that happen, either you cut something away or you create an offset.
