keybinding configuration is not working

[c02y]

This is all my configuration about helm-gtags:

(custom-set-variables
 '(helm-gtags-prefix-key "\C-cg")
 '(helm-gtags-suggested-key-mapping t)
 )
(require 'helm-gtags)
(add-hook 'c-mode-hook 'helm-gtags-mode)
(add-hook 'c++-mode-hook 'helm-gtags-mode)
(add-hook 'asm-mode-hook 'helm-gtags-mode)
(with-eval-after-load 'helm-gtags
  (define-key helm-gtags-mode-map (kbd "t") 'helm-gtags-find-tag)
  (define-key helm-gtags-mode-map (kbd "h") 'helm-gtags-find-tag-from-here)
  (define-key helm-gtags-mode-map (kbd "o") 'helm-gtags-find-tag-other-window)
  (define-key helm-gtags-mode-map (kbd "r") 'helm-gtags-find-rtag)
  (define-key helm-gtags-mode-map (kbd "s") 'helm-gtags-find-symbol)
  (define-key helm-gtags-mode-map (kbd "f") 'helm-gtags-parse-file)
  (define-key helm-gtags-mode-map (kbd "p") 'helm-gtags-previous-history)
  (define-key helm-gtags-mode-map (kbd "n") 'helm-gtags-next-history)
  (define-key helm-gtags-mode-map (kbd "z") 'helm-gtags-resume)
  (define-key helm-gtags-mode-map (kbd "S") 'helm-gtags-show-stack)
  (define-key helm-gtags-mode-map (kbd "u") 'helm-gtags-pop-stack))

But all the define-key part is not working at all, if I disabled

'(helm-gtags-suggested-key-mapping t)

the prefix-key (C-c g) is not working.

So what is the correct way to redefine prefix key and keybings at the same time ?