I've been using Artool Ultra Mask. I think it works well and I've been buying it in a 9.5" wide roll. That should work in the Cameo if you're wanting to use it by the roll.
I've been preferring to cut pieces and using the sticky mat, that way it's less likely to move around.
I have some Oracal 810, purchased from Oramask® 810 Stencil Vinyl – CraftCutterSupply.com
I bought the Ultramask from Artool Ultra Mask Professional Masking Film (midwestairbrush.com)
Dave