Heater core leaking into back passenger floor board

I need help accessing the heater core properly to most likely replace it as I’m having warm wet carpet in the back floor of the passenger side. I feel fairly confident it’s the heater core as it’s warm to touch and I’m not building proper pressure in my coolant tank. Plus I notice it’s a steady drip coming from the A/C drainage line in the fire wall. I thought it was a clogged A/C drain issue at first but I flushed that line out and it continued. I’ve put some coolant stop leak in as well (flush out several times prior- I have good water flow on both sides). I’m pretty sure in the slow drip coming from the drainage in the firewall there was that glitter they have in that bars leak liquid aluminum stop leak. Though I’ve always thought the floor would be wet on the front passenger side not the back seat area. The front is wet but nothing like the back is now it could be from when I’m parked at home I’m parked on an incline so that might be causing it to just run back there I don’t know. But I need to know how to affectively access this darn thing, lol. I’m going to cap off the heater core in the meantime as well. I’m going to use the flush T from a flush kit and connect the two heater heater if you think that’s fine. I’m going to put the rubber caps on the heater core ends out of the fire wall as well. I honestly want to replace the evaporator core while in there. What are your thoughts? Anything else in that area that’s difficult to get to that should be done at the same time? I’ve replaced a lot of the actuators already. There might be one in that far right corner of the evaporator core that I haven’t replaced.