EGT should really be measured before the turbo for accurate readings.
The disturbance caused by the probe (thermocouple) would be minimal (probe is about 5mm in diameter)
The reason most put it in the dump pipe is just incase the proble fails and goes through the turbo.
If you plan on doing the EGR blocking mod, the EGR hole in the exhaust manifold is a perfect place for the EGT probe.
Got the A pillar pod from ebay uk (~$AU 30 delivered), but required some minor modification to fit (~1 hr)
To block the EGR on a ZD30 nav, you need to block it off at the exhaust manifold (rear of exhaust manifold), Intake (middle drivers side entry) and swap 2 holes around for the EGR solenoid. Some instructions in here -
egr/butterfly mod - The Navara Forum (somewhere)