Nice Tammi Marder, Pete!
Turns out I am building one of those Tammy's for the Marder Madness campaign! It's a nice kit and a great (IMHO, of course

) builder - stuff mostly goes together well and the detail is pretty good - although I had some AM stuff lying around, so...
My primary disconcerts lie with that 2-piece barrel (which I did use but which caused me some grief) and the kit tracks - which I (luckily had them around!) swapped for some Tristar links.
Looks like you managed to get those tracks on OK - I wanted some sag, myself, but looks like yours fit OK. Your gun barrel looks good from what I can see - again a kit-part I liked least with this thing!
It's a pleasing build. I would offer a couple of suggestions which I think you can hit on pretty easily:
1) Those shell-holders in the fighting room... get inside them with a small brush and dry-brush in some "steel" and maybe some dark rust, or maybe get in there with plenty of dark oil-wash - these tinny things had shells slammed down into them, etc., and should, I think, look pretty scraped and dirty inside?
2) You (and almost I, too!

) carried on that ugly build mistake that perhaps generations of builders have "faithfully" done! I refer to the gun-mount. That trunion rail - that trough-like piece the barrel and breech slide or recoil back along - is alas kitted as 2 pieces which are mated together... leaving an ugly and way-out-of-place seam down the inside middle. UGH! But EASY to fix! Cut a thin strip of alum foil just wide enough to fit inside there between the sides, and glue it in with almost anything - even wet paint. Paint the foil over with your base dunkelgelb, and apply some dirt and grunge and / or oil-wash and you'll look like a champ! This will completely hide that dismal mid-seam!
3) I would suggest getting in with a tiny brush with some very thin dark gray or satin-black color and gently soaking in those periscope-blocks! Those blocks were typically finished in a black enamel (though "typical" does allow some to be other colors...) and they would add a zing to that aspect of these builds.
All of above are of course just my constructive suggestions and opinions.
Looks good and looks like a Marder! Thanks for sharing!
Bob