With all due respect this is about 90% of your problem right here. When skip conditions are marginal, many many stations are well below s5. That doesn't mean you can't work them..... I have an s1 noise floor and regularly work stations coming in at s2 or 3. Is your noise from powerlines or some other source? There is equipment available that can mitigate that noise.. Check out MFJ-1026. It will take s9 of noise down to s1 if it's set up right.i have s5 noise floor where here and use <20w
As far as running under 20 watts output......again, you are at a handicap. I get that legal power in the U.S. is 12 watts max, but the vast majority of the newer CB radios that most people are using now run far more than that. You'll find huge numbers of operators are running Anytone radios (also sold as Radoddity) that put out 60 watts or more on SSB. Ranger and Galaxy radios are often in that range as well and some even more. Even the newer President radios can be easily modified to put out 40 or 50 watts SSB. Some of these radios also have impressive swing on AM.
So you may just need to up your game a bit in order to be competitive on the band. I run about 150 watts SSB and 100 FM and as I said above, it's a rare day that I don't make at least a couple contacts somewhere. And then there's the whole antenna side of it. A poor antenna equals no contacts.