Trademark is generally industry specific, so you are probably technically correct. That may not be enough.
You can bet every Tupperware lawyer would be opposing that mark. You better have lots of money to spend years in court. Even when you're in the right, you can still lose.
For warming them before use I know a few people who recommend a towel heater. Personally I think it's pretty hot when I pull something out and feel it's warmth and know it's my warmth