Installing Hardie board as a skirt

My houses skirting is wood, where as the house it's self is all Hardie board. For living in a very high fire prone area, it seems impractical to replace with wood. I'll be adding additional studs to prevent a repeat of the warping issues.

Question is; do I need to do any prep work for the butt ends? I'm reading just silicone and then paint. But it can't be that straight forward. And any regular counter sinking screws? Only Hardie board screws I have don't sink.

Thanks for any advice!

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