We focus on the integration of STACK--a Computer-Aided Assessment (CAA) technology--in the mathematics department of a high-ranking University in the United Kingdom. We study a department-wide project where instructors were expected to implement STACK into continuous assessment tasks for (nearly) all core modules across the first two years of undergraduate study. We present this work as a departmental case study, drawing on semi-structured interviews with six novice STACK assessment designers (and module leaders), supplemented by students' responses to an open-response feedback questionnaire, and the reflections of a co-project lead (also first author). Our thematic analysis identified four themes related to the design of STACK-based assessments by novice to STACK tutors: the process of 'STACKification', technical challenges, users' perspectives on the role of CAA, and finally, variations in assessment designers' approaches to the role of feedback. In presenting our results, we are guided by Sangwin's (2013) design principles for mathematics assessment. We consider various technical aspects of implementing STACK-based assessments as a first-time user, and the knowledge required to do so effectively and coherently. We conclude with a series of reflections on the role of CAA in undergraduate mathematics, and the ways in which such technology can be productively integrated with established practice.