Wacenturion~
Alright heres the down low on the Chehalis launches and what you need to avoid... The South Monte ramp (the one under the 101 bridge) is a nightmare at low tides. Basically the concrete ramp stops and then it just drops off into the river. I've seen numerous boats lost right at the launch because of low tide issues. As long as you have the water, you shouldn't have any problems launching and pulling out. But stay away from there during low tides, trust me on this one.
The friends landing launch is much easier. The ramp goes down a lot further and it doesn't just drop off when you do come to the end. I've never launched there during a super minus tide, but have during regular low tides and done just fine.
The Cosi ramp is fairly good too during low tides, but there is limited parking and it's usually pretty packed. The 28th street launch is ideal, but it too has it's down falls during low tides. The Westport shipyard is right there, and they use this launch to launch their 100 plus foot yachts. The problem is that they have built up a flat gravel landing that goes a ways past the end of the dock. So when you have a low tide you really have to back down a long ways to get your boat off the trailer. I know I have had to back past the dock and really jack knife my trailer to the side to find water deep enough to get it off the trailer. It can be done, but it's a pain in the butt during a minus tide. All in all you should be all right, just plan around the minus tides... Good luck out there...