How to do pattern matching with trivia (Common Lisp/sbcl)?

I want to use the trivia library and I am using SBCL.

I want to be able to match a Scheme expression:

(match '(let ((n 2)) (* n 2))
  ((letp a b) (list a)))

(defun letp (exp)
  (and (lisp exp) (equal (car exp) 'let)))

I have tried to create my own type:

(match '(let ((n 2)) (* n 2))
  ((letp a b) (list a)))

(defun let-p (exp)
  (and (lisp exp) (equal (car exp) 'let)))

(deftype letp ()
  `(satisfies let-p))

I have done it like this:

(match '(let ((n 2)) (+ n 1))
  ((guard x (list-p x)) (car (cdr x))))

The above works but I want something cleaner.

Thanks