Now that I've got org-caldav working (thanks David), here's a simple helper function so that the files specified in org-agenda-files are exported. I hope it works for others too!
(defun org-caldav-set-files-from-org-agenda () "Set `org-caldav-files' from the files specified in 'org-agenda-files'. Ensure however that `org-caldav-inbox' is not included in the file list." (let ((files (org-agenda-files))) (when (member (file-truename org-caldav-inbox) files) (setq files (delete (file-truename org-caldav-inbox) files))) (setq org-caldav-files files))) (org-caldav-set-files-from-org-agenda) Stephen