May I point out with a little tongue in cheek, that Douglas Adams wrote 5 books of his trilogy.
They are:
The Hitchhiker's Guide to the Galaxy
The Restaurant at the End of the Universe
Life, the Universe and Everything
So Long, and Thanks for All the Fish
Mostly Harmless
I felt they were hilarious, although the humour may not be to American tastes, particularly the references to the game of cricket. However if D Adams could produce a trilogy of 5, I'm sure others could also.
Cheers, barbarosso