Looks like the main difference is 2.75in height. Might not sound like a lot, but I keep mine near the cab on the driver’s side under a hanging rack, and it is a little bit of a pain to access because I can’t open the lid very far in that configuration. Hasn’t stopped me or anything. Still works.
I’d say, given the increased volume, if height is not a problem for you, the 45 is a lot more fridge.
Wish I’d made a cardboard fridge or template like @androo , instead I agonized over it for a few days and then bought the bigger one on eBay.