I have an existing outdoor 50A outlet connected to a 50a subpanel with a 50A breaker which is currently mounted on the side of my house (previous owner used it for power to his RV). I want to move this line about 150' down to my lake to power a 240V 3/4 hp aerator and also run a 120V circuit another 75' from this junction to power a light and outlet for my dock. Here is what I plan on doing so far:
Run 3 #6 THWN and 1 #8 THWN ground from the 50a subpanel to a 3R outdoor enclosure. I will bury the wire 18 inches deep in 1" schd40 conduit for the 150' run. I plan on installing a 2 pole 15a and 1 pole 20a circuit breakers in the box.

Connect a outdoor weather enclosure for a 240V connection for the outlet for the aerator.

Run 75' of 3 #12 THWN in 3/4" conduit for the lights, switch and 2 110 outlets (GFCI).

My questions are as follows:

What type of outdoor enclosure will I need for the 240V aerator outlet? The current 50A outlet has a metal outdoor weatherproof enclosure but I can't seem to find any faceplate for that box that I could install a 240V outlet in (the only 240V outlet for my type of plug I can find is the same size as a standard 110V outlet).

What size of wire do I need to run from the new sub panel to the 240V enclosure for the outlet?
Any help would be appreciated - Thanks.

 

I am not sure without looking about the faceplates and enclosures, but, the number 12 will work for the 3/4 motor and you need a bigger pipe for the run for the number 6. 1 1/4 minimum as at that distance you will have a real problem getting the wire pulled thru. No one ever regretted using a bigger pipe size.