It was pretty simple, actually (and I know "simple" is a relative term regarding someone's experience and skill, but I'm an idiot, so compare it with that baseline). The seat came with 4 bolts pre-installed and hanging down, so I drilled 2 holes in the cross member that is just outside the battery box and the bolts line up perfectly with those holes. I then cut those pre-installed bolts to a manageable size and tossed some nuts on the ends, bingo. It doesn't move around at all. If anything, I will add another cross member to provide more support and prevent any possible sagging of the seat.
If you want pictures, let me know, I'll post some tomorrow for you.