Smoke in cab - burning eyes

New batteries

 

Take the cover off the battery compartment and take a look. One or more of the batteries will be wet on top, or very hot to the touch.

 

Rotten egg smell. Sulfur

 

Check the exhaust on your bunk heater. there is a rubber gasket between it and the cab where it mounts, they do deteriorate also check the clamp where exhaust pipe mounts to heater.
on older models it is a flex pipe material
Could be leaking, also intake for heater usually has same flex pipe and both are notorious for leaking after awhile.
Also if wind is blow just right it will blow exhaust from heater back under cab and bunk heater will suck up the exhaust in to intake and blow into the cab. May not be your issue but worth checking

 

Idle your truck, run the truck heater pulling in fresh air, roll down one window an inch and turn off the bunk heater until it is checked out.

Who did the install on the bunk heater?

how is the exhaust routed from it?

 

Could be the alternator is over charging the batteries. That makes the batteries hot and vent gases. Careful checking this, because the vapor could be explosive.
This happened once on my truck. I replaced alternator and the batteries.