With the newer models, putting an aftermarket head-unit (radio) in is challenging. We don't have a lot of choices to mount the things. It seems with the newer models, we have a lot more room there, or at least the opening is bigger.
I'm still very new to Slingshots (bought mine in December of this year), so I'm learning as I go (and reading a lot on these forums). So, I bought the wrong adapter and of course, it didn't fit, and completely fit through the opening, so that's why I say that we have a lot more room.
I had bought two adapters, first one I got in, wasn't the greatest quality, and the single page instructions stated to cut my dash. Like hell I'm cutting my dash. Well, I might have thought about it, if the part was well made aluminum or something, but it was just cheap plastic.
Being that it was cheap plastic, I cut the hell out of the adapter until it fit 
It's not going to stay, just there temporarily until mytoy get's his 2018+ double-din mount done and I'll be buying the first one he sells.
Others had noted that the previous years had the harness to plug in a stereo, and I had purchased https://slingtunes.com/shop?olsPage=products%2Fspss18 for this. Once I removed the cubby on my 2019 base, I found no harness to match this part. I found 2 wires only loose:
The labels said something about power and ground, and they are connected to the key. No other loose connectors that I could find and especially no always-hot wire, which is something I needed for my Kenwood. Here are the rest of the pics I took while I had my phone stuck off into the dash: https://imgur.com/a/0YbM46j
It was late in the day, I was pissed off about other things and didn't take any pics of the radio installed, it's not perfect and not up to my standards, but I'll show pics of the current state in another post. I've yet to connect the USB ports or the cameras yet, hopefully will get to those soon. I'm not planning on speakers, relying on my Sena headsets in the helmets. Well, that's the plan, lets hope they work out long term
