i use a haki brush and paint the emulsion on, and for years i used a foamy paint brush, and it worked just fine.
i never used urethane because it yellows in time instead i use store-bought gelatin for a binder.
sometimes more than one coat of the emulsion works best.
look on alternativephotography.com under dry plates
and also look for the book - silver gelatin, they are both great resources.

good luck !
john