I was goofing around looking at some Dave Christensen stuff and came across this. Talk about a match made in heaven! Apparently they collaborated on at least two projects. I don't know to what extent they knew each other or worked on things other than these two. I haven't found anything else searching the internet. If anyone knows about it I would be interested to hear.

There is one Rat Fink drawing that has both of their signatures on it, called Ride Them Waves. Its signed by both of them, although it looks like a typical Roth work.
rat fink ride them waves (resized).jpg

According to this article, they did work together on a album cover for a band named The Birthday Party. The album is called Junkyard. Excerpt:
The cover art is by Ed Roth and Dave Christensen.

https://en.wikipedia.org/wiki/Junkyard_(album)

It does have both signatures. Cool!

BirthdayPartyJunkyard (resized).jpg

Found out there is an airbrush artist out of Utah named Dave Christensen who did this, not the infamous Mad Dog. He is pretty obscure, not much presence on the internet. Oh well, still cool stuff.