I have been following methods of cake growers for a couple years and most seem to be using aquariums or coolers. Here is what I have always used and it's time I posted it so others can try it too. I "think" it's somewhat original so please pass it on.
If you go to Home Depot or a large hardware center, go to the plumbing area and look for the plastic laundry sinks. There is one made of a PVC material and is about $20. Here is a description: White plastic sink comes with four detachable legs-when assembled stands 2ft 8in tall, the sink chamber is about 12in deep with a 20x20in square opening on top that has a 3/16th inch high lip or rim running around it. The opening MUST have this rim. The bottom of the sink chamber has(of course)a drain hole in the bottom.(see where I'm going with this?) Now, get the sink and take an EXACT measurement of the opening INSIDE the rim on top(should be around 21 1/2 x 22 3/8 inches square)then have a piece of glass cut to that size, line the edges of the glass with duct tape and you have your chamber lid. The duct tape acts to seal the chamber because the rubberized tape surface is resting on the plastic sink while the glass square is lying inside the rim of the sink. If you don't see a place to lay the glass or the opening comes straight up with no rim, you got da wrong sink(look for this rim).
Use the method of your choice to keep the cakes off the bottom. If you do not use a bubbler jar you can fit about 12 cakes in the bottom. The drain in the bottom is self explanatory and you can get a plug to fit it or rig up an external valve on the outside pipe so you don't have to open the chamber to drain it(no more tilting coolers or turkey basting aquariums):-). The plastic sink is very easy to drill into so measure the area for your drip shield, get the glass and hold it up with some screws or something pushed through the sides. If you use the ultrasonic just cut the needed holes. My sink method can't be EXACTLY instructed because every individual has different preferences.
Good fitting glass lid-(no making a frame with plastic).
Elevated chamber-(stands on its own legs).
Drain built in-(obvious advantage).
Fits up to 12 rice cakes-
Adapts to your method-(drill and cut holes with more variety).
Hide your project quick-(is grandma dropping by? Just throw a sheet over the thing, set a vase and a bowl of plastic fruit on top, because its waist high like a table).
Save space-(cut the legs short, make a PVC pipe frame and stack em up). *haven't tried this yet.
I hope some more good ideas come from all this. Good luck,