The peak load is an issue, and that can cause current to be drawn back from the sevcon. There have been issues with some EV builds in the past with DC to DC burning out as they act as a small reservoir of power to the main controller and they burn out. . Same with doing this with an Inverter. Never try and use it when the Sevcon is connected. Its just not worth the risk. If all else fails simply use a pair of Anderson connectors. One on the pack one on the inverter. Check the inverter is fused on the inlet many/ most are. If not consider a Midi fuse they are fairly compact, and the std inline fuse holder will do 150a. with 6mm connections you can use on crimped cables. Check the holders though some have small cable inlet mouldings. And Never, Never solder any of the connections, always crimp. If you cant properly crimp, get someone else to do it. Its really important.