I was in similar situation (link), but had a few extra requirements. I needed to move the outdoor enclosure further away from where my old controller was (it would not fit there) and I also needed to split the control wires between the new zone valves in the ground and the old "master" valve above ground.
For my project I've used one, four port, water proof junction box and some flexible waterproof conduit. Overall I'm pleased how it came out. You can find pretty much all of the components within electrical aisle of your local home improvement store.
Let me know if you have any questions, and definitely keep us informed on what you end up doing. Looking forward to seeing what you come up with