There are a few guys talking about improving the coolant lines on the gtm kits and I thought I would post up a simple solution that requires only $0.60 and WILL make a big effect.
First off I want to put it out there that noone has actually had a problem with the lines the way they come some just want to improve it. If you have a gtm TT kit and you have actual proof of boiling the coolant in the turbo line, or have recorded the drivers side chra temp as over the max spec from garret post it up and then I will change this paragraph. There are many kits for different vehicles that run lines like this with no problems such as the aps, and i think the hks 350z turbo kits so it is nothing new, and because the line runs through both turbos it actually has a stronger thermo syphon effect in the hose due to having two heat sources pulling on the coolant when the car is off. Also lets not forget that water has a tremendous capacity to absorb heat and that the turbo bearings(the important bits) are actually being cooled by both the water and the oil circuits.
Now for the actual modification. This is something almost anyone can do it is very easy and there is no crimping or anything involved, all you need is two 3/4-1" hose clamps or factory constant tension clamps. The way the 370z and g37 heater hoses are run is that the passenger side is supply and the drivers side is return. All we will be working with is the passenger side hose. the factory "union" in the passenger side hose is actually a flow restrictor for the heater core to improve circulation through the core itself. In the GTM instruction manual this union is swapped for the the tee for the turbo coolant feed line. The reason the heater core circuit is used in the first place is that there is a good pressure differential across the two hoses. Because of the restrictor in the passenger side hose the pressure on the engine side of the restrictor is higher than the pressure on the heater core side. What you do here is instead of removing the restrictor, you simply cut and instal the coolant tee in the straight part of the hose between the restrictor and the engine. This way the the pressure differential across the turbo coolant line circuit will be greatly increased meaning more coolant will flow through the line to cool the turbos and the best part is there are no pumps to fail or anything. Also when the car is off it will be much easier for the turbos to syphon coolant because it wont have to go through the restrictor to get to the tee.
Edit: for the instal manual just google it thats what i did think i searched "GTM Turbo Instructions" Also I had originally posted this in somebodies thread when they were discussing it but he had the mods delete it. Also the miata guys do this and you can actually buy different sized restrictors online if you want. The smallest restrictor that still lets your heater get hot is the best one to run.