After reading over the instructions again, I came to really like the idea of a relay mounting board for my rear relays and terminal blocks. So, I procured a piece of 1/4 inch polyethylene (basically, cutting board material) from a local supplier and cut it into this shape:
The exact dimensions are not terribly important, but cutting the corners off is, since various bumps, protrusions, etc. in the rear compartment make it difficult to fit a 10 by 10 square piece of anything.
Here it is with the terminal blocks and relay box installed:
And here is the whole assembly placed (but not yet mounted) in the engine compartment:
Although it looks like almost no components on this board connect to each other, it is still worthwhile for ease of mounting and visibility.