Question about using Poplar as Build platform

[RTLdan]

Hi Everyone!
Sorry if this has been asked elsewhere -- I'm going to be trying to print with some Taulman 618
soon. Went to the wood store and picked up the dimensionally closest Poplar board I could find to Taulman's 12" x 12" x 3/8" recommendation which ended up being 12" x 8.5" x 1/4". Not ideal, but I think I can make it work? It's square so it looks like I'll be able to clip it down ok.

Anyhow, now that I have the wood, I realized that I didn't know if I was supposed to set the wood on top of the glass, or right on top of the onyx. Additionally, do I want to heat the wood up for use with the taulman, or should I disable heater bed?

Ideally, I would have bought Garolite, but it runs something like $40 before shipping at McMaster last time I checked...
So I wanted to give this $2.75 board a try first.

Thanks for your help!
-Daniel