Can I reduce draft in an elevated floor with house wrap below the insulation?
Yes it would. I've built a number of &quot;four season porches&quot; in Minnesota (for high-end clients who would've certainly complained if their floor was cold). They're essentially rooms on posts. Our standard approach is as you describe--fiberglass batts with house wrap below, then treated plywood. As long as the house wrap is securely pinned to the floor framing you'll effectively block wind.
Section view:
================================== &lt;-- floor sheathing
~~| |~~~~~~~~~~~~~~~~~~| |~~~~~~~~
~~| |~~~~~~~~~~~~~~~~~~| |~~~~~~~~
~~| |~~~~~~~~~~~~~~~~~~| |~~~~~~~~ &lt;-- fiberglass insulation
~~| |~~~~~~~~~~~~~~~~~~| |~~~~~~~~
~~| |~~~~~~~~~~~~~~~~~~| |~~~~~~~~
~~| |~~~~~~~~~~~~~~~~~~| |~~~~~~~~
---------------------------------- &lt;-- house wrap
================================== &lt;-- treated plywood

Since you're reversing the order of the outer two layers, I'd maybe use 1x2 battens and screws around the edges to really pin down the house wrap and create a seal.