There are multiple ways to make the bed top. Many people just use plywood. I go the extra mile and make a frame out of metal electrical conduit, do a rope/string type hammock design for the top, and secure it to the frame using elastic cording. This makes an ultra comfortable, breathable bed.
The real trick is in the legs. Since many floors aren’t flat, you need to make each leg a custom length to keep your bed level.
I wouldn’t go with a power station, they’re under powered and over priced. A house battery will be much cheaper, and much more useful & versatile. Charge it while driving via an isolator, relay, or solonoid. Some people add solar, but I haven’t needed it.
The problem with power stations is that they still need to be recharged, and it’s not unusual for them to take 6-8 hours to recharge. My house battery charges MUCH faster than that!
Fridges are expensive, unreliable, energy hogs. The propane ones are okay, but I’d skip any that also require electrical power. I got an old 3-way out of an RV for $50, and converted it to run on a liquid candle instead of propane. Now it only uses a few ounces of vegetable oil a week, and I have a large fridge and separate freezer that really keeps things frozen.
For many years I chose to just use an ice chest, they’re cheap, easy, reliable, and foolproof. A 99¢ block of ice would last me over a week, and picking up ice on my normal grocery runs was no big deal. During the hottest parts of summer, I would simply wrap it in a moving blanket to make the ice last longer.
Storage under the bed is always a great solution.
You didn’t mention climate control… To stay comfortable year round, you’ll need climate control, both heating & cooling. There are many options available. You can also get heating/cooling clothes, blankets, & seat cushions. Many will run via a USB power bank. I like to charge all of my electronics as well as my house battery when I’m driving. That makes my house battery last longer.
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