... that actually has a horn. So few Rhino helmets/skins actually bother with helping him look like his namesake, and usually make his head seem very tiny against his broad frame.

I love the Thrak helm on base Rhino, but the uncolorable white section and lack of metallics make it awful on Prime. The Scarab Sect and Mastodon skins add horns, but they also use the Accent channel in ways that don't mix well with Rhino Prime's base skin.

Rhino's not exactly the most popular frame to design for, but that makes an open opportunity!