[Concrete]

Dremd,
hope all is well
I'm sure everything is not full speed after the Evel Knievel Vibe event

butt.... I have some data from using this cool-or-heat seat for a week or more that might be of interest to you (and maybe MazdaMatt and the "cool towel")

putting aside the slow thermal electric issues and issues with my particular seat cover there are some basic problems with cold tubes and butt cooling I have discovered.

The seat cover I have has a very thin cover of nylon between me and the tubes so keep this in mind as I relay my issues

Condensation is a problem -
it might be less thru a thicker layer of leather - but I can see the wet outline of the cooling tube path after I have sat & sweat on it.

Cold tubes can be very uncomfortable to sit on -
perhaps for a cool shirt that lays on your skin this is acceptable
but when gravity presses your arse & back into a cold tube that is wet with sweat - it is almost painful
I have had to turn this wimpy thermo-electric cooler off because it was uncomfortable after it starts getting cold.
even when I was in a hot cab and sweating (yes this is an odd feeling)
this is compounded by the insulating properties of the foam around the tubes
it seems to focus the cold into narrow uncomfortable channels
if you are using ice water & an 8 loop system it might drive you out of the seat
your leather seats may mitigate some of this
also wondering if smaller tubes (capillary) and more of them might help.

A cold seat (towel) may not be enough-
I have used this seat cover in hot conditions and it is not enough (even when full uncomfortably cold) to keep me anywhere near cool. This cover is only cooling about 2 square feet - but I have to use the air-conditioner as well. In conjunction with A/C it is nice to have a cool seat - without A/C you sweat
not sure I have even turned the A/C down much

just a heads up before you start cutting on your seat
you may want make a cool towel type temporary mockup for a few drives before you commit.