1. Jon is correct. Do NOT try to use "Legal Zoom" or other computer boiler-plate legal programs to set up a trust for an NFA weapon. Some folks did, was in the wrong format for that state. problems with the BATFE.
2. Yes, it is possible (and legal if you do the paperwork FIRST) to make your own suppressor. Unless you are a skilled machinist, and have access to a lathe/ milling machine, it is a bit more complex than you might think.
3. That 2 liter bottle does not work as well as you think- but it WILL get you 10 years in a Federal Pen and a $250,000 fine if you do not have a paper from the BATFE with a $200 stamp on it, and a SN on the pop bottle. Yes, I'm QUITE serious.
4. While a can can be a lot of fun, if you are into .22's, first, go buy a box of CCI CB Longs, and a box of Aguilla Colibri, and try them out. Legal, quiet, cheap, no fingerprints to file, etc.