The symex-traversal form accepts a single traversal argument. If you’d like to do more than one thing, then wrap the steps in a maneuver or a venture.
symex-deftraversal is equivalent to (defvar name (symex-traversal traversal)). As it uses defvar, once defined, you cannot use the same form to redefine the traversal (e.g., if you are debugging it). You will need to use setq directly — e.g., replace defvar with setq in the expanded version of this form.