I had to modify the hat so it would fit on his helmeted head. I cut open the band and added an extra band made of vinyl leather. I made the two belts out of strips of this same vinyl leather, using the buckles from Kroenen's original outfit. I also used one of his original knives, but painted the sheath black and added some metal fittings with epoxy putty. Aside from that, all I did was to remove the shoulder boards from both the jacket and trenchcoat and add the patches to the collars of his inner jacket. The Panzer trench coat is actually a very dark green, which shows up if you put the figure in sunlight, but otherwise it matches pretty well. Unfortunately, it's too small for him to wear over his other clothes, so I went with an "over the shoulders" look which I think works pretty well. I also needed to use one of Darth Maul's hands because the normal Kroenen hands couldn't hold the luger pistol.
If anyone wants to know what I used, here is the parts list. It came to a little over $30 without shipping. Of course, there are probably better alternatives for some of these things, and I can't guarantee that you can get the same parts that I used, since these places have limited stock.
Toy Anxiety
ITPT Panzer Trench Coat $3.99
Johann Sigel Patches $2.99
Sideshow Angel Leather Pants $4.99
War-Toys.com
Balthasar Bobby Woll | Pistol w/Holster $2.25
ITPT Von Rudstedt | Ironcross $0.45
Vassily | Leather Jacket $9.95
Willi Bauer | Hat $7.95