When I was playing with liquid emulsions last year I had issues with the stuff washing off too. what i did was use "glossy polyurethane varnish (not satin or matte)". I found it on the Liquid light instruction sheet and it seems to have solved the problem. I've used it on wood, glass and the cheap artist canvas that A C Moore sells. I picked mine up at a hardware store in a spray can for $5 or $6. Maybe this will work for you also. I know there may be a difference between the LL and cyanotype adhesion but it's worth a shot.
Also i found that applying a quick light coat and waiting until it was tacky (about and hour) then applying another coat and letting dry for 24 hours worked best for me.
Hope you figure something out.