It looks like you could just declare them as vars. Certainly don't declare them as VECTORs or ANGLEs--that would just complicate things, especially because you're only changing my.pan in that function. According to your code vars would be fine--or if you want to be more Lite-C-like, you could use int, double, float, etc.

function rotate_model(var rot_angle, var rot_speed)
{}