How do I build this access door?

I need to build an access door for a kneewall space (it’s got a radon pump in it). The kneewall is a closet wall for a few feet, so it doesn’t have to be beautiful if I put it in the closet. It does have to be relatively sound, air, and heat tight. I thought about sandwiching some rigid foam between plywood, but that seems like a lotta work for a door that won’t be used much.
Does any company premake such a thing?
I also thought about just cutting an entry 16″ wide centered between two studs and screwing down a piece of rock. Given that I won’t be in there all that often, this would work, but if there’s a better way I’m all ears.
Pete
Replies
Not the same application, but close enough. A few years ago had to do something similar in a dormitory. The "door" was plywood and sat under the desk where your feet would be. Behind the door was simply a stapled batt of insulation cut to fit . The plywood overhung the opening about an inch around on all sides, which gave room for a lip to sit on. The lip was weatherstripped with el cheapo self stick foam, and since access was going to be once a year, four screws held them in place, one in each corner. The ply was finished to look like the rest of the desk unit. You could pretty easily grab the bailing wire, pliers, & duct tape and rig up something equally as elaborate. If it's drywall inside and you want to make the attempt at hiding, MDO has a paper face and at least when painted wouldn't stand out like a sore thumb.