I pretty much don’t do any clean or permanent stuff, I like to play with subs, boxes, amps, so it’s hard to just install something and forget about it. You guys should have seen the mess of wiring in previous vehicles.
That said, here is my plywood board so the amps aren’t laying loose like I was guilty of doing for many years prior.
1/2" plywood, with some small 2x4’s cut to shape to mount it to the back seat area. Also gives a little room for extra wiring, the crossovers for the front door speakers are also tucked back there. The wiring is mostly accessible when I pull the rear seat out. This is in a 1995 Lincoln Town Car which has an odd shaped trunk. I wasn’t sure where I wanted to position the amps on the board, so I ran the wires over the top of it instead of drilling holes to put the wires through for a proper look, was supposed to be temporary and then remove to drill the holes, but never redid it. I also wasn't sure if I wanted to mount the crossovers there too, but just ended up not doing that. I did not have any carpet and was not about to buy any, so it got spray painted black with some left over paint.
I do need to pull this out though, the amps are getting old and the switches need cleaned, maybe some other problems as well like RCA cables, but I haven’t felt like doing it. Has needed to come out for a few years and just haven't felt like messing with any of it.
At any rate, just a quick scrap wood rack to get the amps up out of the way. I do use my trunk to move / haul stuff sometimes, so any sub or subs usually have to come out at some point, so have never went for anything permanent. While this isn't great, it at least looks somewhat okay at a quick glance, and it works for its intended purpose = amps not laying loose.