The only way any suit could prevent you from being seen by a thermal imager is by preventing any leaking of body heat. Not possible. A good thermal imager can pick up footprints some time after you walk over a parking lot, even if you're wearing heavy boots. No matter what you're wearing your body is going to leak heat, and a temperature differential between you and the environment will show. The only 'tests' I've seen of clothing designed to defeat thermal imagers have used the cheapo commercial models. The $15,000+ models the gov't has are much, much better- I've used them to track bad guys at night, and they are really impressive.
That chemical suit will actually cause your body to produce MORE heat, which will leak out the neck, arms, and legs. You'll stand out like a flare. And no, taping the openings won't help.