I just found a small thermos which is cylindrical and has a screw on cap plus a cup(good for holding the developer). Target $5, in the camping section. Looks like it would hold 4x5 and maybe 5x7. They have larger ones too. Since it has a thermal interior it might maintain temperature so there may be no need for a water bath except to spin the thermos. Motor base may work too. Might even be good solution for the semi-stand development crowd. Haven't tried it yet.