I  have a newly built addition to my home (in process). Crawl space will not be vented, with an opening from my heated basement through a former window opening. this opening does not provide enough room for access due to a waste line.  I have  two openings for access from the outside, and am insulating the walls in the crawl space. I want to make the openings air tight. What is the  best method to use?

I am in north Jersey, so we have humid summers and cold winters.

It has been suggested that I frame out the opening and place basement sliders in backwards, or close the openings with wood and adhere insulation to plywood. Any suggestions would be appreciated.

                                                                  Thanks,