I also have a VersaCamm SP300.
Just a forewarning, I've tried Roland's HTM in the past and it had a fairly heavy hand and I had some problems with wear and tear, this was about 2 years ago, so unsure if they've changed their material since then. Solutions Opaque from Imprintables seems to be the best I've found as far as printable dark heat transfer vinyl, but I haven't tried very many.