I got a P238 HD today, and will be installing one of my stainless triggers in it. When I do I'll also do a step by step photo record of the process for anyone who wants a steel trigger instead of the plastic one.
It looks like that mainspring housing is either plastic or aluminum, in either case we will be planning on making replacement MSH's of 416 stainless with serrations.
Maybe I'm the only guy who hates aluminum alloy in my guns, I dunno. The sights on this gun are tritium night sights, very nice, and they are made of blackened steel.