I use biscuits to build hive boxes. I now have have 8 year old boxes with zero failures or warping. I use 3 #20 biscuits for deeps an 2 #20 biscuits for mediums. I cut the rabbet end pieces to the inner dimension of the box, and run the side ( 19 7/8") pieces past. The biscuits cut to the end of the rabbet pieces, and the side of the long dimension pieces.
I cut the biscuits on centers that are symmetrical, so the pieces can be flipped in during construction.
For mediums, I use cheap 8" fence boards ripped to 6 5/8th. I look for "loss leader" sales on fence boards- You can pick them up for about 1.50 per piece on sale. The biscuits add about 16 cents per box, purchased in bulk. I put in a drywall screw to tighten up the glue up. Use Tightbond 2 or 3 for waterproof glue-up. I use a carefully calibrated diagonal stick during drying to keep the box square. One fence board builds one box 2x 14.5 and 2 x 20 = 70" (approx with kerf).
I heavily paint the exposed end grain on the side pieces. I think keeping the rabbet end grain protected prevents the end boards from warping outwards, as the tend to do in the finger joint design.