I have used these thread inserts for the access panels on many enclosures I have built. They are not cheap and I recommend using epoxy to seat them "permanently". Chase the threads if necessary, after the epoxy sets up. The pic is linked to a manufacturer's site, if you want to see more or find them locally.

The problem with using them on a Wicked One is that you will need so many to properly seal the whole top (or bottom) of the cabinet. I used course drywall type screws, about 80 of them, on my Wicked One builds, but obviously if I had to open the cabinets very often I would strip the screw holes, eventually. I think my screw holes are three inches apart, but you could probably get away with fewer, depending on the type of seal you use. That's the main issue - it must seal perfectly. How you do it is up to you.

T Nuts flipped over will act the same as the threaded inserts- although they would defineatly need to be epoxied in.  

Another option is the use of draw bolts such as these:



With a cut out like this:


You would have to drill through the top for the bolt, then router out a hole in the side of the panels where the rectangular bolt would slide in.  Then the bolts are tightened from the top and pull the rectangle upwards, which tightens the top down.  It would take a little time, but a simple jig or template could be made for the router to make the rectangular holes in the side panel.  They could also be made larger- so as to make it easy for the bolt hole to be drilled and hit the hole.  

The holes are usually made like this on the underside of countertops: