1. Cut the MC4 cable and butt splice marine wire to it. But this voids the warranty on some panels. (But I doubt if anyone has ever collected on a solar panel warranty).
2. Buy a single MC4 extension cable. Cut it in half and plug each end into the existing cable and splice marine wire to the cut end. This is the preferred solution as it lets you easily disconnect the panel (for servicing??? or whatever).
Ok, I've looked at the tools online now.......I can see this if you're going to put together thousands of these connectors, but to do a handfull you're able to do almost exactally the same thing with a normal ratcheting crimper or even solder and pliers.
I know it's not 100% up to spec, but come on, really?
You can disconnect them without an MC4 Assembly Key, but having one makes things easy.
This durable plastic MC4 key is very handy for both the assembly of custom MC4 wires, and also for breaking connections after they have already been locked together. For extension wire assembly purposes, we recommend using one key along with a V Jaw style pliers.