I've been researching and delaying my build for ages, but now it has to start!

A little background my name is Wim I'm from the Netherlands and my wife has MS and is in a wheelchair, until now we have been camping with 2 dogs and my daughter in a Sprinter van short wheelbase and a drive away awning.
The living space in the awning is quite small when it rains (it rains a lot here) and i need to move the bed chairs all the time, so I've been thinking to make a tear/square drop just for sleeping 2 persons to gain some more space in the awning.
Now here my issue most diy campers are with a kitchen in the back and my plan is to use a slide out bed that slides out of the back of the camper so i can lift my wife onto the bed and slide the bed inside. so I'm sorta stuck with the construction strength of a bed that slides (with heavy duty drawerslides) out at least 48 inches (120cm).
I haven't even been thinking about my kitchen lay out yet because of that slide out that i want to tackle first.
Greetings, Wim.