Boris Katan is busy building a booster for his Hell Boy, which is a 19x24mm clustered PoleCat 5.5" Fat Man. The booster will add 31 24mm motors, bringing the total motor compliment to 50. The booster is single use with the 31 motors glued together and butted up to a plywood thrust plate. The fins, as shown in the attached photo are three large tubes. Read all about it over on TRF.