To me a ground cloth is only good if it's waterproof and most materials ARE NOT. Do this test with your tyvek—
Go in the back yard and turn on the water hose and create a small puddle in the grass. Turn off the hose. Put the tyvek (or any other ground cloth) on top of the pool and spread it out. Sit on it for 5 minutes. If any water comes thru with this weight (hydrostatic head pressure), the material won't work and is not waterproof.
You can even try your current thin denier tent floor using this method and see if it also leaks. This becomes important in gully washers, ground sheeting and pooling, and setting on up slushy snow.
