Confusion about “Seemingly not ～”

Question

So there are several ways to express something is "seemingly not ～":

1)  ～なさそう
2)  ～そうにない
3)  ～そうもない
4)  ～そうにもない (is this one even real?)

I was always taught ～なさそう in my Japanese classes, and it was not until I heard one of the other ones that I ever become confused about them.

After doing a little research on this, it seems that adjectives can only take ～なさそう. ex.

○ 料理がおいしくなさそう
？／×　料理がおいしそうにない

but that verbs can take any of the forms

○ 雨が　降らなさそう／降りそう（に・も・にも？）ない

So, my questions are a) is the above reasoning correct, and b) what are the differences/nuances of the forms in 2,3,4? Someone please set me straight on this; it's been bugging me for a couple years.

Answer 1

Looks like you have done your research well. You are correct with verbs only taking そうに/もない。Although そうにもない　is not grammatical though.

雨が降らなさそう　you make an assumption based on current state of the sky.
雨が降りそうにない　you have confidence that it wont rain (due to some extra information maybe).  
雨が降りそうもない　you want it to rain but it seems like it wont (from extra information or from appearances)  

There is another common way to express the same idea, ～みたいです。only used in the affirmative. (ie, 「～みたいじゃない」ってだめです）

あの男の人は学生じゃないみたいです　on campus you plainly state that guy over there doesn't seem like a student.
雨が降らないみたいですよ　when you heard a broadcast or checked the web. よ shows your confidence here. But...
雨が降らないみたいですね　is similar to 降らなさそう because you are looking for agreement with ね

Answer 2

I just realized I didn't know the difference so I asked a native Japanese.

Here is the explation

降らなさそう

normal straigh meaning: "it doesn't seem to rain"

降りそうにない

this sounds like: "I though it would rain, but now it doesn't seem so"

降りそうもない

this is like the previous but も makes it more strong, like put an "absolutely" in front.

降りそうにもない

this is correct (same meaning that 降りそうもない) but a bit too complex for casual conversation. It's かきことば.