AC filter

I've got a charcoal filter with finer media openings than stock, that can be cut to fit.
When Coleman repaired our rear ac last of June, I asked about using it. He said they would rather that we sued their filters. Air flow restriction. Gave uss aan email address and they sent us two for free.
W keep our coach really clean inside and don't cook anything that throw off a lot of grease vapor. When we do cook we open the fantastic vent fan too.
I've washed the stock filers ay times over the years a real pain if any grease vapors get into them and it will destroy the material.
I'm not sure what basement air units use but it is time for a redesign for quieter unis with enough filter area for extreme filtering.
The idea was that most RVers didn't take care of things like filters and didn't want problems with the ac from not servicing filters. We need big enough intakes to use the super small micron filters like we use at home, and a filter for the dash air.Lot of junk comes in on a thousand mile trip behind trucks hauling dirt, plowed fields,and such.
Perhaps you can try it and report back. Kind of measure flow from the ac before and after you install it.

I normally trade my class A in when the filters need cleaned or changed

I use this now http://www.homedepot.com/p/Flanders-PrecisionAire-24-in-x-36-in-x-1-in-Permaire-Pad-Air-Filter-40655-012436/100178722

How often are you changing the foam filters out....??

Yes they are washable but after couple times they begin to stretch

Thin foam material is used because of airflow requirements......if return airflow gets restricted icing can occur on evap coil

Buy a large bag of foam material (ACE Hardware etc) and cut out several filters
Then change out routinely/as needed.....that could be weekly/monthly/bi-yearly just depends on use and environment

Clean dirt ones by soaking in soapy water....rinse/dry/store. Then discard after a few uses.
Foam is cheap..but effective when kept clean and not stretched out

Foam filters don't filter very well so they need to be cleaned often. I wash mine after a week of operation. It does help if you use filter spray which helps with holding the dust and pollen in the filter rather then letting it pass on to the coil.

I just bought filters at an RV dealer in Las Vegas (Johnnie Walker)and they are only like three dollars. Out of one you cut it in two and you have filters for both air conditioners.
They work pretty good on my air conditioner/heat pump units.

But then again my coach is pretty well sealed and not much dust gets inside the coach. Some coaches have very poor seals around the slides etc.