I finally sourced a quality Boxster spare tire, and started exploring storage options. For starters, it doesn't look like the spare will fit upright in the frunk:
but it will fit on a slant, thereby negating almost all of the storage space.
Two possible places in the trunk: straddling the rear deck,
or on top of the engine cover.
With the spare on the engine cover, I noticed no interference with my rear view in the mirror. For trips that require luggage in both the front and rear trunks, I think this will work best, as long as the spare is securely tied down with some sturdy rubber straps.
For just tooling around town, I may opt for the rear deck option, as I use the frunk frequently.
TO