I have a 2019 Crew Cab with the 19 (supposedly) speaker HK system. I've used Crutchfield alot in the past and their service and free installation parts (like harnesses) are awesome and thie prices are decent and never had an issue through them with compatibility but they offer (currently) no solutions for the subwoofer behind the rear seat. Under the subwoofer category of "What fits your truck" they have for $185 : JL Audio C5-525cw-RP. Would those be a good substitute for an actual sub in the rear? All 4 doors would be uber expensive, but what if you just did 2? I'm thinking of doing a few things I read here, like putting the poly fill in the sub in the rear (you dont pack it tight right? Just loose?) and deadening the bolts with some sort of padding or double sticky tape as mentioned.... I also am seriously considering upgrading some key speakers like the door and dash, but does anyone know if the 2 in the front door are component speakers fed by a common feed? That would make upgrading them super easy with a decent set of components. Or does the wiring get messy and have multiple leads coming from the AMP?