Thanks for the ideas guys. It is a stock Nissan ECU that will be mounted:
So I don't need any access to it once it all up and running. The harness enters on the passenger side where they usually run the AC lines. No AC in this car.
Under the seat is a good option, but even though I did a good job fixing and sealing the floors, I don't like the idea of having electronics where they can get wet. Plus, my harness is not long enough, and I don't want to lengthen it because it has some shielded cables that I would rather not cut into.
I'm thinking about behind the glove box. The was mention RHD cars having a lot of room behind the glove box. I would think that LHD drive would be the same.
Thanks,
Pete