It all depends on the type of bass you want really. If your looking for "I can hear you 5 blocks away" then get anything from 500-800w If your looking for good all around bass including surround sound, then get something around 150-300w
I used to have a jl 10" in a single cab truck being powered by 150W 1ch. amp and it was fine for me. Keep in mind that my setup was different because it wasnt in a trunk the speaker was in the cab with me making it louder naturally. I also had a single cab small truck with not a lot of space.. this also made a difference because I was sitting on the speaker, so to me it was pretty loud.