Question about sealing seams on cab

[Metalaroundstone]

I have had several leaks that have penetrated through the plenum assembly that goes across the front of the truck just in front of the windshield. Many of these leaks caused rust inside my cab (cowl) up underneath the dash. All this was damage was very hard to cut out and repair since I am not doing a frame off restoration. IMO the plenum system is extremely problematic in terms of the longevity of the cab. The air intake grill essentially allows anything smaller than a field mouse to fall into the plenum which then either gets stuck in the plenum or on the little sills above the air vents, or at the top or bottom of the fender.
Question #1: Has anyone figured out an attractive way to reduce the crap than fall into the plenum.

Question #2: Shouldn't I use seam sealer on the joints between the firewall and the plenum assembly? I can't tell it this joint was sealed from the factory. See pic below.

Question #3: Should I use seam sealer on the joints between the plenum and the cowl. See pic below. I don't think this joint was sealed at the factory (except for the vertical one), but it seems to me it might be helpful to seam seal this joint except for the area behind the windshield wiper stubs. Opinions appreciated about this.

I also included some photos of my process of fixing the rust in the plenum, staring with cutting a access hole, cutting out metal, replacing metal, and welding up the access hole. Even though the work was in an area that will never be visible to the eye, when I was finished you could not tell it was not from the factory except for the seam sealer I added.