Getting a King mattress into a Liberty or Independence
would be easy since it would be compressed/rolled/folded. Just set that big 'taco' down where you want it, remove the outer plastic, and watch as the mattress unfurls into a ginormous 75" x 80" x 9" field of comfort.
What could possibly go wrong?
#1 Getting a King mattress OUT of a Casita.
Can't be done. The ceiling height in a 17' Casita along the center aisle (minus the air conditioner and fan controls) can't accommodate a 75" tall mattress standing on its end, nor can it be manipulated around the kitchen and entry door curve. Oh, and the entry door isn't tall enough.
#2 Putting on bottom sheets is a wrestling match.
Many owners can attest to the difficulty getting a Full size bottom sheet on, much less on a Queen or a King.
Colorful language is common during these bouts.
#3 There's only one place for one person to sit inside and that's on the edge of the mattress, in the aisle space, where your feel (or someone else's) will be smack in front of the fridge door and furnace vent (if installed). And it's raining...
#4 There's no way to get to the lower compartments because the mattress(es) have made it difficult to access the water pump, water heater bypass valve, fresh water tank, and converter (power supply / breakers and fuses).
Here's an idea for the LIBERTY or INDEPENDENCE:
Order the 1703 INDY set. When you feel like honeymooning, set the tabletops down into the bench grooves to form your platform, then push the mattresses together for 60" total width and 80" length.