On the metal machines there are vents at the front of the floor that can be closed off.This works well (close in warm weather, open in cold weather). The air will still blow under drivers floor and out the engine doors for cooling.
If your Machine has a gassy smell in the cab,this may be a leaking exhaust gasket which should be fixed for obvious reasons. To ckeck for leaks run your hand around the manifold when the engine is running cold,you'll feel a puff of air where the leak is.
If you have an oily smell in the cab check your pcv valve.On my old woody I've run a 1" piece of rubber hose from the oil filler tube on the block to a vent on the fender ( stock on the woodys ). This keeps all the smell out of the cab exept the odd spilled rum.
I have a piece of carpet on the floor in all my machines,this cuts the noise down. I may spray the under side of the floors with box liner spray to reduce it even more. Or just put in a loud sterio.
Stuk-n-slush