THe instructions say to put the solenoid under the front seat.
I installed in a 1992 Lumina ApV. I put the solenoid on the passenger side fire wall, Then cut a piece of plywood to fit over it.. Wife never noticed it was there (She rides shotgun) even 6'3 by 300+ pound me had enough leg room to not be bothered by it.
IT need not go under the seat.
Home is where I park it!