My only experience with Kadee running boards is applying them to Red Caboose '37 AAR box cars. The RC car comes with wood running boards and my M&StL box cars should have Apex and USG running boards.
The underside of the RC roof is cored for hole locations which match the Kadee pin spacing. I drilled out the first roof with loose holes and superglued the running board in place. It immediately buckled upward giving me a 'wavy' running board. That surprised me because before gluing the running board lay flat.
Now I drill the RC roofs with a press-fit hole, use no glue of any sort and have flat running boards. Not only does this seem to work well but it speeds up the project some. I am doing 35 RC '37 AAR box cars lettered for the M&StL representing cars from four different series. Now that the Superior and Equipco hand brakes I need are both available from Red Caboose I can do them right.
The reason I continued on with the Kadee running boards rather than trying something else - and I saw some good ideas in this thread - is because I had already bought 50 Kadee running boards and didn't want them to go to waste.
