RE: CL model towing a glider?
You know the arguments about locating the CG for pitch stability and how lethal a CG can be when too far aft?
Consider the problems you'd encounter with something attached to a CL model. Whatever the item, a banner or glider or such, is going to encounter the same centrifugal forces the tow plane encounters. If the glider is on lines, then that problem is partly solved. If the glider isn't, then maybe the glider needs to be R/C controlled if only to trim it to fly around in circles with the least problems for the tow plane. In either case, the tow line probably should be attached at the Neutral Point of the tow plane so it'll cause the least steering effect.
I'd think the most important problem to solve would be how to get the glider/banner to track with the least effect on the tow plane.
Experience with R/C planes towing gliders convinced me to go instead to cradles for the power plane to carry the gliders aloft. You can't imagine how badly the glider pilot can affect the tow plane if the glider pilot doesn't know what is required and can do it. And setting the gliders trims so it could be towed without a pilot's input really doesn't seem possible to me. And that's possibly what some might want to do for this CL deal.