Build a box the size of the frames. You can go for as many frames as you like, but 10 is a nice number. 1x4 material is about the right size. Make two slots for the 1x2 slats.
Stock the ends
glue and insert tops
nail the tops
flip it over
glue and insert the bottoms, then nail. Nailing at an angle keeps the nails from pulling easily.
Pull the slats and dump them out. All done.