Rifle silencers don't need to be cleaned so long as you aren't shooting exposed lead through them.
My choices for a 300blk can would be something with a large diameter like the 1.75" offerings from Q, Sig or Dead Air. I'd personally go with a Dead Air Nomad, and that'll give you a lot of other good options should you decided to use it on other hosts later on. I also would look at the Q Trash Panda/ Half Nelson. If you want it to be more quiet than those offerings jump up to one of Q's longer options. The larger diameter silencers seem to be where it's at for 300blk subsonic use. I think the Q full nelson is the quietest can I've heard, I personally picked up a half nelson to save on length, and a Nomad in probably my next purchase.
Bfish: I will take your suggestions into consideration. Thanks