I personally have use chemical proof heat shrinks, however when they loosen up with age your wires end up being exposed...
Better to use crimps, then slide the hard cover off.. heat up the metal, fill with solder and slide the cover back on.
DO NOT BYPASS THE ECU, you need the trigger from the ECU that goes into the OEM fuel pump relay... if you bypass the ECU and your motor stalls, the fuel pump will keep pumping... in the event of an emergency you don't want that especially when fuel leaks are involved and heat.