For outdoor weatherproof boxes - Do they make a weather proof equivalent for the NMT clamp connectors that you would typically use indoors? If using screw connectors for pvc pipe to join to an electric/junction box when the cable enters the box is there a way to "secure" it at the entry point? (Essentially doing what the clamp connector would do)

I am running a 240V circuit in my shop for an air compressor and a mig welder. Each device will need a 30 amp breaker. The devices will be located in different areas of my shop. To save on wire and coduit, I'd like to put two different outlets on the same circuit since I will only use 1 device at a time. I plan on running 3 wire (two hots and ground) to each outlet. Can I wire these outlets on the same circuit just like 120v outlets? I plan to run 3 wires to a junction box at the first outlet. Split each wire and running to a set of 3 to each outlet. Is this correct? Anyone have a rough diagram?