you should buy the fiberglass door finishing kit.

https://www.amazon.com/Therma-Tru-Kit-Mahogany-Fiberglass/dp/B00F1ZR1VA/ref=asc_df_B00F1ZR1VA/?tag=hyprod-20&linkCode=df0&hvadid=241889826421&hvpos=1o1&hvnetw=g&hvrand=11505929010722257630&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9002012&hvtargid=pla-529241271586&psc=1

"Also, is there any trick to matching it to real wood? The wood stains much darker than the fiberglass with my test samples."

Unfortunately it will never match wood exactly as the stain does not truly absord. Fiberglass doors typically get stained with a gel r wiping stain and the stain sits on the surface as opposed to wood which sucks up or absorbs the stain.

Our painter used Thermatru's Cedar stain kit. We were able to see samplea at a local Thermatru distributor's showroom. The stain colors shown on Thermatru's website are of very little help.

Hi, We have 10 fiberglass doors with fir grain in our home. Our painter indicated that he always uses Zar stain and poly on them. This is Zar Early American stain. I tested tons of stain colors and am quite happy with this one. The doors were just stained last week. The Zar stain was hard to find. Masonite used to make a door staining kit as well but they discontinued it.

The before and after on the doors

Hi Angela these are beautiful. I am in the same situation in looking for a good stain for fiberglass door. Can you please share the specific stain used in Zar brand? Should I be looking for one specific for fiberglass door? What does poly mean? Any help is truly appreciated. Thanks in advance.