Proace,

I am assuming the the plane is to be flown as a glider, and the motors are just to get up in the air. If this is the case, then reducing drag is probably the most important goal. There is no benefit to using the propwash to enhance lift for a glider. As BMatthews says, getting the motors and props behind the wing is probably best. If possible, I would strive for an even smaller profile than an engine nacelle. If the weight of the motor allows, I'd like to see a short 'sting' jutting straight back from the trailing edge, with the motor in a very smooth pod on the end. I don't know how well a folding prop would feather in this configuration. There might be a tendency for at least one blade to droop down into the airflow, which would not be good. This could be a showstopper for this kind of configuration.

banktoturn