Alan:
I see that you have un-earthed that great pic with the Gebrgs Flak 38 mount! There are a couple more pics "out there" of that particular vehicle - though I can only posit this with the sad caveat that, whilst I have seen them on the Web over the past couple of years, I neither saved them nor their location (site)!
It is certes one of the cooler tricks done to an RSO- and photo'd too.
Over the years, I have come across also pics of twin MG-34, a drilling mount (I believe a 1.5cm version as seen in the SdKfz 251-21) but without any shields, and maybe also a 2.0cm flak on what I thought was a naval pedestle mount. All of these are one-off field shop tricks.
There are also a few pics of RSO with various guns simply packed on - which of course are also all "one-offs".
I was probably overly-loose in my use of the term "mount" and "mounted"- as I had included these latter non-fixed applications in my statement, and did not mean to imply that there were either "production" or formal, refined mountings of most weapons. Sorry 'bout getting anyone's hopes up on that! My bad.
Couple things come to mind- one is that there were some 28,000 of these trucks to play with, 2) there is a pretty good record showing the Germans were nothing if not adaptive and opportunistic and were seen to put all sorts of guns on any type of transporter, 3) actually, we should be amazed that we have hardly ANY photos of any of these things, as the NAZIs were pretty un-forgiving of even their own fellows taking pics of stuff, that, and later-war there was less and less opportunity to have a camera or get film or get it developed. That said- pics of any of these bits are the "where there's smoke..." indicator of a wealth more of field innovation going on!
I don't actually expect Dragon or anyone else to produce kits of hardly any of these field-expediencies- though that Flak-Panther and Berge-Panther / Pz IV Turm do, to some extent, put the lie to me! Dang! wouldn't it be the bees's knees for some Big to make that rig you've posted the pic of!
My position on the RSO is that we modellers are probably quite free to freak with it! So, I am thinking of placing a Flak-43 in a bed... or maybe a 3cm Flak 103/38? Or something. How about a really "last-ditch" "Mad Max" thing with a brace or 3 Panzershreck on a mount- a sort of RSO Wanze, if you will? Maybe a "Pupchen"? A good base kit is out there for all sorts of plausible stick-on weapons... what we need is the RSO on the table.
Cheers!