While not "RK Scale" I have also found, among frameless tank cars, that the RK "modern" tank car (in appropriate private-owner paint schemes) blends in pretty well with its Premier siblings. In real life, one can frequently see 1:1 tank cars of wildly varying size next to one another, and the RK/Premier relationship works well to re-create that effect.
For that matter, the RK Airslide hoppers are nearly indistinguishable from the Premier versions. Like the tankers, the challenge is finding them in non-fanciful paint schemes.
---PCJ
