I've looked at them too, from VTS. I've found them elsewhere online, but they always seem to be made by the same mfr, I think from China. One post that was helpful said that to add insulation around the icebox helped a lot, but you can't easily add to the door. We use a coleman electric icebox that runs in the truck while driving, and then is transferred to the trailer, if we are somewhere with shore power. It plugs in. Not pretty but keeps half and half cold.
Wherever you go, there you are