The AC kit instructions say, "Install all Relay with the terminals pointing DOWN to prevent condensation from seeping into the Relays at the terminals." This, I thought, was a good idea. Even better would be to put the engine compartment relays (the only ones likely to be exposed to substantial moisture) inside a waterproof container.
This is the container I found at Home Depot. I cut out the four internal supports that I did not need, to give me more room to work. Also, I cut a slot on the internal support at top left, because one of the relays needs to have its tab put there to give me enough room to work when I wire it.
Here's the box with the relays in place. The neutral start relay is the big relay at top left. The secondary charger interlock relay is the smaller one at the bottom. The regen relay is the one at the top-right (this relay turns the brake lights on when the regen function is active. Tim has changed the wiring here somewhat to instead activate regen when the brake is pressed. I'm starting with the original and will adjust as needed).
And here is the box in its approximate final location, the driver's side of the engine compartment (note the wires coming from the harness where the engine relay board used to be). Also, note that all the relay terminals do, in fact, point roughly down, just in case any condensation makes its way inside the box.