it's practically all they did
i suppose the cover version can be a means of showing-off one's radicalism or extremism, a modernist(ish) move rather than a postmodernist one
along with Eugene Chadbourne (who carried on doing quite a few covers in his solo career, if i recall right), Shockabilly also included Kramer. As in Shimmydisc, whose whole thing -- or to be fairer, semi-whole thing -- was a kind of ironic yet genuinely yearning replay of the Sixties. Kramer, as in Bongwater.
That's a Monkees cover. (Kramer's other half in B-water was Ann Magnuson, who came out of Club 57 and that whole Klaus Nomi/B-52s/John Waters-y Mondo-irony-kitsch thing).
And Shimmydisc as in B.A..L.L.. Who to my mind always teetered just on the wrong side of the same line that Butthole Surfers teetered just on the right side -- the line being that threshold where the past in pastiche become problematic
The first Shimmydisc album that came into my ken was a compilation called The 20th Anniversary Of The Summer Of Love. There was one really amazing trippy-but-not-too-retro track on it but for the life of me I can't remember what it was or who it was by-- but purely on that track's account, I kept the CD for years and years. Not sure if I got rid of it or still have it in storage