Still could not find a skid plate for the little duke so I bought a Givi RP5103 which is really for a BMW F800GS after seeing this thread:
2016 KTM 390 Mini Adventure (Duke) Build | Adventure Rider
User motorcity ktm mentions that a friend offered him an F800 skid plate and they made it work on his duke.
I never found a plate that looked very much like the one they used, but most of the skid plates for the BMW were pretty pricey. So I settled on the sub $200 Givi.
No special tools to do this really except my dremel and probably 6 cut off wheels (because I am impatient).
The top edge (foldovers) on the right side of the plate had to be relieved for the coolant lines and a relief had to be cut near the top corners of both sides for my crash bars.
On the lower left I had to notch the BMW plate for shift linkage clearance and further back more so to clear the kickstand.
I have not made a front mount for it yet so only the 4 holes underneath are being used (after being drilled to match the duke's existing mount holes). On the forward two bolts the givi plate came with a shouldered spacer that I placed between the duke and the plate and then used some givi included screws along with a flat washer and half of a givi rubber spacer below to tighten it.
The duke uses a shouldered bolt on the air dam so I drilled my rear holes large enough for the shoulder to go through and reused the original screws. Rear screws mount directly to the duke (no spacers).
I am not much of a fabricator, but it worked out ok and I'm sure some of you guys could make a neater install of it.
With only the 4 belly screws holding the plate it is pretty solid. Although I will come up with at least one forward mount for my own piece of mind.