Epic DIY - a lot of good info here although I have just finished harassing PTF and TorqByte myself - Alex is great
And here is how I have designed my fail safe. Boost solenoid patch from JB4 (can buy this alone from BMS). Relay that is default open and then the GPO to default closed. This way if anything fails boost will be cut even if its the CM5-LT itself or the relay
BTW - a TMAP patch can be used from BMS also if you dont want to tap into the factory harness.