I tried a Tyvek suit. Didn't work for me.

If you plan to use the suit as raingear you'll have to seal the seams and that's a PITA. And the zipper is not waterproof. And I agree that the fit sucks.

And good luck when you need to go #2 <img src="/forums/images/graemlins/grin.gif" alt="" />
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If you only travel on sunny days you will never reach your destination.*

* May not apply at certain latitudes in Canada and elsewhere.