Those sliding slat beds are the absolute pits. They’re a pain to build, and a pain to open/close. That design was scrapped 80+ years ago for better alternatives until some idiot reintroduced it to make people think he was a genius. He wasn’t.
Sofa/beds are simple, cheap, and easy to make. Much easier and cheaper than those slat beds. The most comfortable ones do not have flat seats or backs. The L is tilted backwards so that the front of the seat is higher than the rear, and the back is at an angle as well. It only becomes level when pulled out into bed mode. Comfort is pretty high on my priority list… I have built a number of variations of this design, and can probably help you with your design if desired.
Depending on your space & design, a futon sofa/bed might be a great ready made solution.
I’m not very impressed by the power station linked to. I don’t like the fact that they aren’t being up front about exactly what battery it has. If I’m doing my math correctly, 48000mah=48ah. 178wh/48a=3.7v !!! That would be roughly the equivalent of a 14.8a 12v battery, but offering much less power due to the conversion process. That’s not much power. I wouldn’t trust it to run your fridge reliably.
I would suggest a DIY power station using a cheap ~100ah 12vdc deep cycle battery. That would give you 4-6 times more power, for a comparable price. It won’t have the inverter, but the one on that power station is more for window dressing than actual use. In either case, you will likely need a charge controller to go along with your solar panel.
“Everything should be made as simple as possible." ~ Einstein