What is the classification of the hazardous location?
I am confused about needing an explosion proof horn, explosion proof seal and only a type 4 cabinet? The entry into the cabinet doesn't appear to be an explosion proof method either. Plus the mounting of the horn is just bolts through the cabinet wall. If this were an environment requiring explosion proof methods you do not drill holes into enclosures and still maintain the explosion proof rating.
If this is a class 2 hazardous location - the horn will need CL 2 rating - and the one pictured may be rated both CL 1 and CL2, but should not need the sealing fitting, no hazardous gas will be inside the raceways or enclosures for class 2 installations, which is what the seal fittings are for.
Simple duct sealant is sufficient for sealing raceways when leaving a class 2 environment.
Class I, Div 2, Grp C&D.
It is a type Z pressurized/purged enclosure. The mounting bolts have washers on the back side under the nuts inside the enclosure to maintain the environmental rating, although how water or anything else could get into a pressurized enclosure like this through the tiny opening there escapes me.
The hole you see the elbow going thru below the seal is actually thru the side wall of a leg stand, not the enclosure. There is another elbow on the left side of the floor stand kit that turns up and enters the enclosure thru an XP sealing hub.
I think you need a real XP seal between the enclosure and the horn, since the horn is only rated for CL 1, Div 1.
They make a CL 1 Div 2 horn but the guy that started the job did not buy that one. I think with that style of horn you might well be allowed to use some other sealing method, although why it would need to be sealed at all escapes me other than that the code would appear to require some kind of seal between a Cl1 D2 area that is the outside of the box, and the unclassified area inside the enclosure.
I do not do enough of this kind of thing to know the cheapest solution to this type of problem so did what I was sure would work. The fiber dam and sealing material cost more than the fittings did.