This part is open on the back.  

If you want to seal it off, cut a square 12.5" piece of MDF wood to seal it off, using the base of the pod for a template.  
Typically whatever surface you mount it to will seal it off.
 
Speaker hole is already cut to accommodate MOST 10" speakers 
SPEAKER IS NOT INCLUDED

(see dimensions on ad listing)

Made in the USA

We also sell rubber trim for the base to seal it off
The rubber trim can be found here on ebay:  266097387987

This spacer is made of ABS plastic