I've never been much of an allergy sufferer, and according to Doctors in this area that treat for that, I'm living in allergen hell.
And most of the year, I live with the windows open and a whole house fan churning. So special high $$ allergen filters for the AC system, stay on the shelf at the store when I pass.
If you're looking at doing this mod on a truck that's been running for years without a cabin filter, I would definitely clean the Evap coil in the process.
Available locally, pick up a can of 'No-Rinse' Evap coil cleaner (under $10).
Various brands, don't know one that's better than the others, probably mostly all the same. https://www.lowes.com/pd/WEB-Green-W...ner/1000024695
Spray on foam, let soak, then the water created on the fins when running the AC, rinses off and out the drain tube.
If it's never been cleaned before, you're likely to find what looks like matted up dog hair on the fins. The foam may need some help. Use a soft bristle brush to wipe the fins and not bend 'em.
An old toothbrush works great.
With a clean coil and fresh filters, should be GTG.
For more $$, there is a charcoal-like filter available that might be an improvement for allergy sufferers, but a good cleaning and fresh normal filters goes a long way.
2007 LBZ 3500 LT3 DRW Crew Cab, Sulastics, Putnam XDR 15K, B&W 30K-Turnover GN+Companion, Ride-Rite Air...EFI'd by Rob
2008 LMM 3500WT DRW Crew Cab, 8 'Flat/GN, Workforce Alum Toolbox, Ride-Rite Air Use-ta Haves 2006-6.0 3500 WT DRW ExCab Flatbed, 2005-LLY 3500 LS DRW Crew Cab, 2002-LB7 3500 LS DRW Crew Cab I Live my life in such a way that when my feet hit the floor in the morning...Satan shudders & says "Oh shit, he's awake!"