base plate question

Logically, you'd want a Roadmaster base plate, but as a practical matter you don't. Other brands are adaptable. So what you can do is go to the manufacturers' websites and pull up the exact instructions for the plate for your exact Malibu. In some cases, the height where the towbar attaches is different. So you might be able to use that to your advantage. Pick the one that's least invasive and take the instructions to your regular body shop or mechanic. A dealer service department can do it. U-Haul installs hitches, I don't know if they'd do a baseplate. There's a lot of bumper/fascia work on baseplates.
I trust myself. So what if it takes more time than a professional shop might take? I'll get it to fit and I'll make sure every fastener is in place, tight, and secured with Lock Tite.