With velcro, like ATTICUSSER said go straight to the foam, any other coating can weaken the strength. This will sound like overkill, but I buy the 3m self-adhesive velcro (heavy duty or industrial strength). On the foam, I still use hot glue to attach the pieces (peel the adhesive backs off too first lol)., gluing both the back side and running akind of a weld seam around the edges once it's stuck down. Otherwise the self-adhesive can pull away from the foam.
It will work fine with non-adhesive backed as well, I just buy the sticky stuff because I use it for other stuff too.
Last, the heavy duty and industrial velcros do a REALLY GOOD JOB of holding, to the point that you can tear your foam at the attachment points when you pull your seam apart. So, I use more velcro than I think I need, and then trim off hooks from the 'male' side (usually at the center) until the sides pull apart how I want.
It will work fine with non-adhesive backed as well, I just buy the sticky stuff because I use it for other stuff too.
Last, the heavy duty and industrial velcros do a REALLY GOOD JOB of holding, to the point that you can tear your foam at the attachment points when you pull your seam apart. So, I use more velcro than I think I need, and then trim off hooks from the 'male' side (usually at the center) until the sides pull apart how I want.