I have been using 15 gallon plastic induction tanks for about a year now with great success. The only modification I have made to them is using LD Carlson's Better Bottle Racking Adapter installed just as you would in a better bottle carboy. I have not had a problem at all with this system as the racking adapter is easily removed for easy cleaning. The only downside to these induction tanks is that they are not able to be pressurized, but on the small scale it is not that big of a hassle. However, I am currently putting together all of the equipment needed for my 3 bbl brewery.
Due to the low cost of these tanks, along with the approval from the Washington State Dept. of Ag, I have been thinking about using them. Here's where I run into problems. I'm fairly positive that I can get these to seal where they could hold up to 20 psi. The problem lies in the holes that I'm going to have to port into a tank. One for the racking arm, one for the thermowell, two for the immersion chiller, one for the co2 port, and one more for the cip. That's six hole that are going to have to be drilled with at least two of them below the liquid line. Times six fermenters, thats 36 holes I have to worry about sealing, not to mention the 12" lid.
I have found some very nice SS pieces that are very sanitary that would work great, but I'm just worried that some time during the course of using any one of the tanks that I might run into problems with and I really dont want to have that happen with 100 gallons of beer sitting in it. Anyone have any advice for me? I really dont want to have to spend $1900 a pop for SS fermenters if I don't have to right away.