I am seeking opinions as to how to best introduce a 110v power plug into my enclosed car hauler trailer so I can run battery tenders, ect while my trailer is parked.
My trailer has a floor mounted winch battery & I thought about coming through the same box from the bottom of the trailer......

 

I would use a small load center inside the trailer and use a power inlet to backfeed a breaker in the load center. I would just mount something on the side of the wall.

 

I once wired an enclosed gooseneck for shop lights and power tools...

mounted a small Square D breaker box in the front and dropped an in-feed pigtail down from it with a 30A 120V plug on it...

First choice was to put a 240V plug on to run both sides of the breaker box, but we didn't have a generator at the time with a 240v outlet on it.

it's just like wiring a house for an earthquake.