Those cheap Chinese lights need to be thought out better. There is no one stock part to simply mount them to a proper box. You'll need to make something up on your own. Some of the ones I've seen at the supply house have been put together with a plate from the manufacturer with a rubber sealed connector already installed.
You'll need to mount the bracket to a gasketed weatherproof blank place, then knock out or drill a hole for a rubber cord connector of the proper size to pass the cord through the metal plate.
If you do not have the light yet my strong recommendation would be to find one that is already set up to mount to a box properly.
You can't do that
You cannot come off a 30A breaker with #10 wire (so far so good) and then terminate it at 15-20A receptacles. (nope, nope, nope!)
Unfortunately people sometimes become aware of the rule that allows 15 or 20A receptacles on 20A circuits, and they falsely generalize that to "Any receptacle <= circuit capacity". Nope. The receptacle ampacity must be an exact match to the breaker: 15 to 15. 30 to 30. 50 to 50.
Now there are two exceptions, but they are... exceptional.
- 40A receptacles do not exist. NEMA, distributors/stockers, and electricians didn't want the burden of yet another socket type (there are like 40 varieties already when you consider every iteration of 3-phase, 208, 480, etc.) and oven manufacturers didn't want consumers stymied by a 40A range's plug not fitting an installed 50A socket. So the (only) correct receptacle for a 40A circuit is 50A.
- UL requires all 15A receptacles to be internally rated for 20A. As such, 15A receptacles are allowed on 20A circuits.
And that's all, folks!
Only a 30A receptacle is acceptable on a 30A breaker.
"But I want to plug in common devices!" Then you have 3 options.
Change the breaker to 20A.
Now it becomes a 20A circuit (overbuilt with #10 wire - overbuilding is allowed). You can fit 20A receptacles. You can also fit 15A receptacles due to the exception mentioned above.
How do you handle the pinchy wires? I work in metal boxes which are annoyingly small and constantly run out of statutory cubic inches. Obviously your first defense is go with a bigger box. Or go with a box extensions or lids which give extra space. Another option is to place 2 boxes next to each other joined with a nipple -- and in one box, splice from #10 solid to #10 stranded, and in the other box fit the receptacle. Once you work with stranded wire, you won't want to go back!
Install a Power Distribution Unit
PDUs are typically used with server racks. They allow the rack to have a single power cord for the entire rack. It has a NEMA 14-30 or 14-50 plug, and splits that out to a number of 120V receptacles. Mind you, the PDU is a commercial unit that has been through the rigors of UL listing. You cannot build one out of parts except this way:
Install a Subpanel
This is conventional stuff, you bring L1, L2, N and G into a small service panel then hang any number of 120V/15A or 20A breakers off that panel, and those power your 15/20A 120V circuits. In any subpanel, neutral and ground are kept separate. No "main breaker" is needed if the subpanel is in the same building.
Best Answer
A surface mount box can be attached to the exterior siding (what is the siding?) In some cases I like to cut the siding an inset the box and screw it to the sheeting OR cut through the sheeting and make the box flush mount (old work box could be used in this case). Since you have the UF a surface mount is fine I usually use 2 screw clamps, cheaper than a CGB and 2 screw clamps are listed for the UF. a CGB may or may not be listed for use with flat cable it depends on the seal some are hard plastic and those are not on the ones I have used and some are a soft neoprene and some of those are. But I would use the cheaper 2 screw clamp. All the unused holes are required to be plugged if you are concerned with water accumulation it is acceptable to drill a drainage hole in the bottom of the box. The maximum hole size is 1/4”. As far as height NEC 404.8.A all switches and circuit breakers used as switches limit the switch to 6’7”. There are switches that can be up high but these are a specific type not a common snap switch.