Sealant for cab cowl bolts/screws ect

[SkidmoreGarage]

I agree it's always a good idea to improve what you can, but I wouldn't worry about sealing up the individual bolt penetrations through the cab. It's not a submarine, and you will have bigger issues with water coming in from other areas. The window seals, the door seals, antenna, heater box, cowl pinch weld, etc. are much bigger issues that you likely won't solve.

If you just want to protect the bolts from corrosion, some anti seize or quality grease should do the trick.