Let me list what I do here to power up my two 30AMP trailers in my backyard. Maybe it will trigger what you may want to do on your end connecting up to the house/garage.
I run two 120VAC drop cords from my garage to power up my 30Amp fifth wheel and 30Amp OFF-ROAD POPUP trailer when parked here at the house.
One receptacle in the garage is a stand alone receptacle that was installed to run an air compressor at one time and this is the only thing on its circuit. I use this to feed my fifth wheel. My OFF-ROAD POPUP uses a 120VAC receptacle that located near the garage door and is on a different circuit breaker then the one I am using for the fifth wheel trailer.
Before hooking up to the Garage 120VAC receptacle I would use a circuit tester from LOWES -WALMART that looks like this
Do not use the garage 120VAC receptacle if it does not check out "CORRECT" by the correct position of the tester lights...
What I do is use two 10-GAUGE (10-3) HD Contractor type 50-foot that run out towards both trailers. I have used a 12-gauge (12-3) long extension cord with out any issues but would never use the 14-16 gauge "RED ORANGE" smaller size extension cords you find at LOWES-WALMART. They are just too small to handle the trailers.
Out in the middle of the yard I use a RV30A-15A DOGBONE STYLE long adapter plugged into the 50-foot extension cords. These come from WALMART and look similar to this...
I could never use the small round black type RV30A-15A adapters as they always tend to get hot me when used just a short time...
What you don't want to happen is for the adapters to heat up your shore power cable which might end up looking like this and will need to be replaced.
Now all I do is plug the 30AMP trailer SHORE POWER CABLE into this RV30A-15A long adapter laying in the middle of the yard.
To insure the 120VAC power source is safe to use I will use one of these RV PLUG IN 120VAC AC voltmeters (AMAZON) plugged into a receptacle inside the trailer that is in a good view spot so you can glance at it when you need to. This will check the 120VAC level coming from the house. The part I like about this meter is it has a safe zone "GREEN" printed on the face and if the AC voltage is within this safe limit then is ok to use the power - even for one roof mounted air conditioner unit.
I will turn a few thing on inside the trailer for 10-minutes or so and then back outside and check all of the connection points to see they are not getting warm to touch. This includes the garage 120VAC receptacle.
This is pretty much what we do here for our two trailer that is hooked up to the 15AMP service from the garage.
We can run just about everything inside the trailer we want to run but have to watch sometimes what is on at the same time. i.e. we can never run the air conditioner and the high wattage microwave at the same time otherwise it will trip the breaker in the garage.
We sleep in both the trailers all the time when sitting in camp back yard and of course this is where I get to do all my mods and fix up things for the every changing OFF-ROAD POPUP configurations for my emergency radio operations I am connected with. Its a great get away just sleeping over in the back yard sometimes. Wifes gets to use the fridge to supplement her kitchen fridge. Good spot for my beers too...
ALot of folks will warn you about about all kinds things that might happen when only connected to a 15/20AMP service but if you follow some good guidelines like I have listed here you should be ok. Has worked good for me over the past few years.
We use the extension cord and RV30A-15A long adapter when on the road alot. You never know when we may need some power sometimes. Works great when visiting family - I just hookup outside their house and we sleep in the trailer.
Hope this helps
food for thought
Roy Ken
My Posts are IMHO based on my experiences - Words in CAPS does not mean I am shouting
Roy - Carolyn
RETIRED DOAF/DON/DOD/CONTR RADIO TECH (42yrs)
K9PHT (Since 1957) 146.52M
2010 F150, 5.4,3:73 Gears,SCab
2008 Starcraft 14RT EU2000i GEN
2005 Flagstaff 8528RESS