Mine is buried behind a wall with no access panel. Even if I did remove the front of the shelf box, it's sill 16" or more to get to the pump. There's no way to hook up a winterizing kit without tearing out the whole under sink box shelf, then it's still not a guarantee I could get in there to do it. I've done a lot of mods to my camper, this is one i'm not willing to do, air has worked great.
You can just see it peeking around the corner
This is under the sink where the panel would have to be removed. The sink drains are hanging down within a few inches of the top of the shelf.