I absolutely agree with Sheltie's Mama that a sizeable percentage of the population that uses wheelchairs would be better served by Velcro if this is something that is designed to come off from time to time.
As for the snaps, I'm not sure you'll get through 4 layers with the pliers. I tried them on 3 layers of a crepe fabric & had to do a lot of "helping" with other tools to get them to work. The press dye would better serve you with thicker fabrics or multiple layers. I'm not sure how much you'll prefer that over sewing. It is a bit time consuming & you need a wood block to put under the fabric if using a hammer. I got so frustrated that I swore the next time I'm saving up to purchase a table press ... which might be something you consider if you plan to do a lot of these.
Here's more info on all this from KamSnaps:
http://www.kamsnaps.com/Product-FAQs-13.html