Hanging very large, unframed watercolors
We recently hung four large (approx. 7'x10') watercolors. The artist wanted them hung with only one nail in each of the top corners. (I know...) To do this I laminated squares of #300 watercolor paper to the back of each corner with PVA adhesive. These held the weight, but as the paper has moved (expand/contract) due to our imperfect climate control the paper is very slightly tearing- but it's tearing left-right, not down. I tried replacing the nails with linen-lined binder clips but they are not strong enough to hold the weight, so I don't think RE magnets will cut it either.
What other options are there short of putting more nails through the top edge? Is there a material I should've used besides the #300 paper?