I forget what slot number mine was connected to, but it is the rear wiper fuse which is 15 amp. Here's the photo of my fuse box again so you can see how the fuse piggyback is connected:
With the wire from the piggyback going up, the original fuse goes in the slot closest to the fuse box (on the piggyback itself), and the fuse for your new circuit goes in the other slot. You don't have to connect the piggyback to the rear wiper slot but that works for me, and an advantage of this is that a rear wiper failure is not that serious, but something else failing like the instrument cluster could cause real problems lol.
Edit: be sure to check your manual because your fuse box might not be laid out the same as mine.
Good advice :-)
How easy is it to find a solid earth near the fusebox?
I plan to have a go at wiring my Nextbase 402G in at the weekend if the weather is dry.