Hi Allen, found this on Trekwood parts. I hope their customer service has improved; I've not been impressed. But maybe it will work for you:

https://www.trekwood.com/products/655735/Water-Heater-Door-10-12-16-Gallon-Black

Posted by: @thewehrs

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Hello everyone, asking if any one knows the procedure to get a replacement water heater door?  Lost in Alberta as we drive in the mountains. 
We have a 2015 Redwood 39mb2. 
getting it painted to match may be a issue. 
Thanks in advance 

Allen & Kim Wehr 

Allen, 

I MAY have a "spare" door that I could send your way.. I would need the measurements off the opening of the water heater to make sure it fits.  

I had an issue 1-1/2 years ago with my door bubbling so I purchased a new one. The new order never arrived so they sent it out again , I then received 2 and still have the bubbled one.

So, I have a black door, and a painted door that has some pin size bubbles in the paint. I would be happy to send the painted one to you as long as you know you will have to get it painted.. IF a paint shop is gonna paint it, they will want to prep the door anyway and those bubbles would go away at that point.

If interested, I could send it UPS to you and have you just send me the UPS payment in return. 

The issue is I am away until July 10th and cannot do anything till then...

Joe