previously, I just ran an extension chord out to near the systems, plugged in as much as needed (never more that three so far) and placed an piece of tupperware over them.
This year, with an EnF in the mix, I simply tied a loop at the end of the ext chord and hung it from a nail under the EnF table.
No problems so far.

We wouldn`t get away with that where i live :)
I have 70ft of armored cable buried 3ft deep running to my shed. The power is distributed from the shed out to weatherproof IP68 enclosures.

I just chop my pump cord at the plug and crimp the wires to 2 core double insulated cord, insulation tape and heat shrink tube around the join and run that into my house, I have 3 pumps coming off one line as they are all flood and drain and so on the same timer, and 2 other pumps on there own lines, air pumps are all inside and 15 meter airlines (x8) and going to the tanks, not sure how much air is lost per meter though, but doesnt seem to be much.

right now i just have an outdoor extension cord running from a gfci outlet in my garage. i put the power strip and airpump inside of a plastic container, the type that has clips to hold the lid on. i used my dremel to carve out a channel on the side of the box. It's just big enough for the extension cord and airline to fit through, the lid seals tight and the lip of the lid keeps water out.

I covered that with some plywood and so far no problems with water getting in.