How many tubes of RTV should I use...

Why the hell would you need RTV to seal a water pump on a 3.0?
There is an O-ring on the the back of the water pump that goes into the water pipe.
Other than that, I can't think of a reason to use RTV
The water pump has two openings where it mounts to the block. The water pipe at the back with the o-ring is the inlet from the radiator.

My brother has a '92 Duster (mine previously), 3.0, 5 spd
'91 Daytona , 3.0, 5 spd
'94 Shadow, 3.0, 5 spd.
They are fun cars to drive.
There was a '93 Shadow in the junkyard, recently. Convertible. It was really nice. A relative of the deceased owner drove it to junkyard. 'didn't want to fool with advertising and haggling', she said.