You don't need any holes for the canisters, there is a small hole under the rear seat cushion that you can thread the tubing through. The older models did not have the quick disconnect so you had to be careful not to loose any oil when disconnecting but the newer ones I think all come with a quick disconnect coupler so it is not a big deal at all. The hole under the seat is quite useful for other things like pressure tubing for boost gauges etc to thread into the cabin from the engine compartment.
here are some old pics

 

Jean, no roll bar in that wild street/track machine? Not worried about safety?

 

Spartan, you can buy the quick disconnect option. As Basal Skull mentioned, there is already a hole under the rear seats. You will have to make it a bit bigger maybe I cannot remember.

The reservoirs can go inside the engine bay without any problems, as an aside, the GT2 race cars had them strapped to the control arms.

Cadence, I have a bolt-on Heigo 6 point roll cage, I take it out when I drive the car on the street because it is dangerous to have one without helmet, I sometimes don't put it back because I am lazy...and irresponsible

 

Mine are mounted in line with the crossbar member going left to right under the car. Just reach under the car in front of the rear wheels to adjust.