I have used it many times it's a very good product .
I think for a Porsche it's a little over kill to spray the hole inside of the car .
sound and feel is part of driving and owning a sports car and one of the best parts IMO .
as your motor is behind you the need for the heat coating would not be all that much so you would used about a Gal of it out of the 2 gal bucket . it covers about 19 SQR feet per gal.
sound coating will cover about 22 SQR feet you will used the 2 gal. bucket up on the floor pan and rear fire wall area .
I can't see a need for the heat coating on the floor pan as it's a rear engine car so there is no heat from the motor and exhaust running under the car .
even the sound /noise is coming from behind you .
we did a all steel 32 ford coupe with it 3 or 4 weeks ago and we when thru 4 gals of heat coating and 6 gals of sound coating on the hole inside of the car using the max mils they say you can use of the product .