SWMBO left heavy flower pots on each end of our 48" unsupported step
made out of Trex this summer, and the Trex boards warped (very bad--more
than 2").

The design looks poor, so that's where I'll point the blame. ; )

Here is a drawing of the current design along with my proposed solution:
http://web.newsguy.com/MySite/deckstep.jpg

Questions:
1. I would prefer to use screws (rather than nails) to add new
structural support, so I don't cause damage. 2.5", pre-drilled?

2. In the diagram of my proposed solution, I would have screws being
(not) held by end grain. I know that this is a problem.. What is a
smart, easy and inexpensive way to get around this here? It looks like
I need a brace/bracket of some sort. I would like my repair to last! : )

3. One of the new 5.5" wide Trex boards will have to be "ripped" to
4.25". Is the stuff difficult to cut? Can I use a cheap 40 or 60 tooth
blade (do I need to use a router)? The Trex website suggests a 40-tooth
"carbide tipped" blade and/or router, I believe. I can practice on the
stuff I remove, but as soon as I remove any, I'm going to create a
"safety hazard". I haven't even bought the new Trex yet, I'm just planning.

Here is a copy of the SU file, if anyone would care to use it.
http://web.newsguy.com/MySite/DeckSteps.skp

(Thanks)
Bill