I started with the Flying kit, then created my certificate, filled out the different fields, uploaded my certificate, and performed the packaging under Shipping, and it appeared to work in that it created an APPX file.
Below are my screenshots (please note platforms for only UWP), incase it helps any, along with the contents of my FlyingCert.bat file:
"C:\Program Files (x86)\Windows Kits\10\bin\x64\makecert" UEUWPFlying.cer -r -n "CN=RvBGames" -$ individual -sv UEUWPFlying.pvk -pe -cy end
"C:\Program Files (x86)\Windows Kits\10\bin\x64\pvk2pfx" -pvk UEUWPFlying.pvk -spc UEUWPFlying.cer -pfx UEUWPFlying.pfx
pause
.
.
.
.
.
.
.
.
