Thanks for your input. Yeah, the 2010 and 2011 have the central vac input on the wall next to the stairs. I guess different from yours. That's what we were wondering, what is down there? Are there any pipes or ducting in the way? You are saying it would be open to the whole underbelly? Okay, we could built walls to seal it off. I got photos from someone on the forum that had a pet door put in the bottom of the linen cupboard in the bedroom and cats steps that led down to the basement. The cats had the whole basement for a playpen. So we were thinking of a wall-off area like that. We didn't want to put a hole in our cupboard, so we were thinking of something else. When you mentioned neglecting litter box, at first I thought you were talking about me (the box cleaner) but then thought you were talking about the cats. hehe. I've been trying some new litterboxes, at home, and have been moving them around, and the cats (2) think it's really fun. They seem to like doing it in a new place. So they might be okay with it. I know it would have to be easy to get to.
My comment about neglecting the litter box was based on some of the homes I've been in for various fire calls, not directed at you personally. The last one was a bit of a mini-mansion (false reading on CO detector). Three cats and two small boxes in the basement corner with litter (what there was of it) the consistency of concrete. Had to step carefully, if you know what I mean. I couldn't resist, so I gave the person a bit of a verbal lesson on cat care. She had the "deer in the headlights" look. Just don't like seeing animals, especially cats, mistreated.
But, yes, the wall in the kitchen, if you put a door in there, will allow them to get into the underbelly since it is behind the basement walls. Once you pull a wall section in the basement, you'll know what I mean. If you want to give them the basement for a play area, you will need to make some kind of enclosure from the kitchen wall to the basement wall so they can't get down there. It's probably a distance of about four feet between the two walls. And then, naturally, you'll have to be careful what you put in the basement, too. If they're like mine, everything is a toy and it belongs to them. The converter on mine is mounted right behind that wall, and there is a mess of electrical wire. There is plumbing back there, but should not be a problem.
As for the central vac outlet, we had ours installed by the dealer, it was not OEM. They put it in the step riser. In some of the photos I've seen where it's installed by HL, they do put them in the wall. At first I was confused as to why the dealer did that to mine, but now I'm glad they did. Even so, it would not have been a big deal to move the litter box when we needed to vacuum.