You can probably make them any size that suits you, but lighter wood seemed to make sense -- so I used 3/8 inch poplar (not plywood), used some small wood screws and glue for assembly, covered the boxes with the same fabric as the curtains (used spray contact cement), fabricated cording for the edges, stapled this on...and mounted using simple angle brackets (one olympic rivet at each end), and screwed the boxes into the angle brackets. Used spring loaded curtain rods. Only two holes in the A/S for each box.
"SilverLeaf II" 2015 30' Classic
2014 RAM 2500 Laramie 4x4 CC w/6.7L Cummins
WBCCI # 3430-Unit 21