While I was up at 3:30am checking river/flood info, I was going to post a reply. I went back to bed instead.
Yes, using the tri-fold cards is perfect. Michaels may still have them in their scrapbooking area. I have used Aida, punched paper, evenweave... almost anything. I always use double-stick tape from the scrapbooking section... it's acid free and won't leave a stain in case someone wants to frame it. Herrschners may have these cards, too.