If one wants to keep the trailer light and simple (as in "not 2,000 pounds and not complex"), one has to think about it as a super tent that is hard-shelled. A super tent doesn't need running water, a 3-way refer, built-in electronics or a deluxe kitchen.
Depending on where you live (temperature & humidity) and what kind of camping you do (RV park with hook-ups versus dry camping in the woods with or without nearby water), your "super tent" needs will vary.
Mine is set up for dry camping in low humidity. If I am in an RV park with full hook-ups available, all I am going to use is the water spigot and set up food preparation on the picnic table provided or my aluminum folding table. My rig has a small porta-pottie, but I use the RV bathroom for the toilet and the shower. I've camped in places where the only shower was the lake, the hot springs or the creek.
I carry a portable 12-volt AM-FM radio & CD player, a small laptop, and a book. Might get a portable DVD player, but it's not too likely. (Camping is about escaping civilization and being entertained by mother nature...but a little CCR, Willie, Mexican or Brazilian music is my vice.)
Instead of HOW MANY FUNCTIONS / HOW MUCH TECHNOLOGY CAN I FIT INTO THIS TRAILER TO MAKE IT LIKE HOME? you might ask, HOW LITTLE CAN I COMFORTABLY GET AWAY WITH TO ENHANCE THE CAMPING EXPERIENCE IN NATURE?
Side benefits to this approach include, far less money spent and far less time building.
A clear skylight over the bed
majorly enhances the camping experience in my trailer.
FWIW,
Prem

My goal...
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...is to live in a trailer.