it depends...
What do you plan on putting there? Maybe you won't need any access.
I'd suggest not putting anything there, and not cutting an access hole in the top skin if you can help it.
If you are going to put something there, design it so that can easily be removed, and include long service loops so anything electronic can be hooked up on the floor, then pushed back up into place.
Just remember.. whatever you put there, you'll need to access it on your back in the most uncomfortable position ever.