Carp in the coastal lakes, I don't think so, I've been fishing Siltcoos since I was able to walk, and I have never heard of Carp or seen them in there, lots of gas bubbles though, which looks like feeding Carp, Largescale Suckers might be your Carp. Devils Lake is the only place with Carp, and they are stocked + illegal to target, so that doesn't count, lol.
And for Crappie in Siltcoos, good luck finding a meals worth, Crappie seem to be extinct in that lake since the flood of 96, once in a great while you can find a school, but you would have to be dedicated to the lake for that to happen.
Perch are another story, coastal lakes are the place to go, but Siltcoos is also not doing too well for the Perch fishery, Munsel Lake gets much deeper, and has no shortage of Perch, nice Rainbows in there as well, just be careful about the Bull Trout.