I was a bit surprised this morning when I saw this comment…
…these days if you choose multiple products to install on your device from Basecamp they are uploaded as separate img files anyway so you do get one per product.
So I tested it out and sure enough, if you select multiple maps to load at once, BaseCamp’s MapInstall utility not only loads them as separate files but auto-names them too! There is no longer any need to load maps individually and rename them, at least on the more recent Garmin models. You can see this above in a screenshot from the eTrex 20 along with one showing the file structure. I tested this on the 62s as well.
The whole process of loading maps is laid out on the BaseCamp wiki if you need a step-by-step tutorial. Thanks to Rob for the tip!