Hi, what are the thoughts on washable filters, my new Trane TEM4A0B30S31SB came with replaceable filters 18X20X1 does it make sense to use washable? Geo

Hello all! I have a question about my A/C condensation draining system, I have not been able to figure out a practical way to deal with this, and it's bugging me. I will try to provide as much information as possible. Ahem... I live in North Texas, just today hit 84 degrees outside temperature, the temperature in the house climbed to 76 so it was time to switch over to A/C. I don't know the outside humidity off the top of my head, but being March in North Texas it certainly isn't dry. My system is a relatively new installation, installed in 2016. Trane heat pump system. The air handler is in the garage, single return just on the other side of the garage wall. Air handler sits on top of the return duct. The house was built in 1978 and the return duct has insulation on the inside of it. The unit runs fine, cools and heats the house okay until it's below freezing outside because ... heat pump. The only issue I'm having right now is with condensation. I actually started fighting this last year. I might as well start there. Last year, I noticed a bit of a watery smell from the vents. I don't know how else to describe it. Basically if you water a potted plant and then sniff the water that comes out the bottom of the pot. Not mildew, nothing particularly unpleasant, just odd. I checked the condensation drain, it wasn't backed up, so I pulled the filter out and saw that water was dripping from the condensate pan into the return duct. The pan is a plastic type, and there was a crack. Being the lazy fart that I am, rather than getting a quote for pan replacement I figured I'd try the cheap route first. I shut the unit off, waited for most of the moisture to get out of the pan, blew compressed air around the crack, scuffed the plastic with sandpaper and then gobbed some 100% silicone sealant on the crack, forcing as much in as I could. Let 'er dry and I haven't had a leak since. It's only a permanent repair if it continues to hold. As a result of this leak, though, the insulation in the bottom of my return duct was soaked. When the unit was installed, the installers had painted a mastic inside the box to seal odor out or whatever, meaning that the water which had gotten through the mastic was trapped. It felt like a water bed down there. So I cut out the soaked insulation (that actually did smell bad), let the duct dry out, then got some R-3 foam board with anti-microbial properties ... I think. It's pink anyway. I put a new "floor" in the duct, then put sides on, painted mastic at the joints and that was that. At least, I thought that was that. Late at night, trying to go to sleep, the A/C would shut off and I would hear dripping. Great. Sure enough, water was falling right off the evaporator coils onto my nice, fresh, acoustically gifted insulation pad. Louder than a dripping shower. This only happened for a few minutes after the unit cycled off, as the bulk of the condensation would form droplets and come right through the fins on the evaporator. Most of the water was still going down the evap drain. So I lived with it. No more smell, water didn't seem to really stick around in there, and I had cool air. Other projects prevailed. So that brings us back to today. First run of the Spring season, the unit shuts off and here comes what sounds like a torrential discharge of water onto my loud foam insulation mat. Once again, the drain pan is working, but in order to catch this water it would have to block the airflow through the evaporator. The condition is likely worsened by the fact that this is the first time the A/C has been run all year, and it had probably not run in heat pump mode for at least 24 hours before. With the thought in mind that this is unavoidable, I started looking around for where this water will go. The outside of the unit has holes poked in the bottom, appears someone literally just took a punch and gave it a couple wallops, 3/8" in diameter. Of course, in my brilliant moment, I covered these with foam board and mastic so they would not function if needed. If I do open up access to these holes, the air handler will suck air straight from the garage into the house though. Not sure I want that, especially because that's a source of more humidity. I could make a stainless steel pan and place it in the duct at an angle, direct it toward these drain holes, and work out some sort of one-way membrane valve for the drains, but I don't want to spend a lot of time and money on that if there is a simpler solution. So my question (finally, gosh) is this: For an air handler/return system like this in a garage with insulation on the inside, what is the correct way to deal with condensation in the return duct? As I was typing this novel, I began to question the necessity of any insulation on the bottom of the return, as the duct sits flat on the concrete slab. I don't want the duct rusting/rotting out, but the dripping sound is also quite annoying. The condensation missing the pan and dripping straight down is likely not a new thing. The coil is not freezing, the unit does not run for a long time to cool the house down right now, and most of the water is making it to the pan and out to the drain. I most likely did not hear any dripping before the condensate pan cracked just because the water would have been hitting fiberglass insulation painted with mastic rather than foam, which amplifies the noise of water droplets better than what should be possible. There is also really not much water making it to the floor, regardless of how it sounds. If I opened up the "drain holes" in the side of the duct, I doubt any water would actually drain out without putting a sloped pan of some kind in the duct. Any suggestions or professional input would be great. Thank you!