It's done all the time, just not in autos. Cogen power plants use steam generated from gas turbine exhaust; ships and remote facilities use diesel jacket cooling water & exhaust gas as the heat source to distill fresh water.

On US Navy CGs and DDs, the waste heat boilers sitting in the exahust from the 2.5MW gas turbine generators (2 normally online) generate 150psi wet steam, used for H20 distillation @ 8,000gpd, hot water heating, cooking, etc for a crew of 400. Also has the nice side effect of reducing IR signature a by a few hundred degrees. FFG7 class uses diesel jacket water- 2 x 1MW generators normally online, distilling & heating 4000gpd.

The problem with a variable heat source (the ICE in a truck) is that you will see a lag between when you call for the extra power with your foot and when you get it, measured in seconds. The engine has to burn the extra fuel, the steam needs to absorb that extra energy, then transfer it to the turbine...each process has its own lag. If you're mostly at a steady load then its not so much of an issue- a truck would indeed benefit more than a car.