We generally use solar MC4 connectors. If you have bigger wires then you can use well drillers butt-splices, called Sta-Kons or DryConns. These will keep it dry until you take it apart... You can also make your own with Mil-Spec adhesive lined shrink and some butt splices. If a system is going to be up for long periods I generally use water proof butt splices. If it comes down each year then I will use MC4 etc...