Out of the box
I know you said no change to towing vehicle, but consider this:
I bought a 2017 Ford Transit LWB (148”) passenger van for about $23,000. Took away the seats and put together a bed, casette toilet, plenty of storage space for 2, foldable table and seats, butane camping stove, off-shore AC. Everything is removable. It is my daily driver and given me over 15k miles of comfortable travel in one year. Total conversion cost way less than $2000. You will have a second set of wheels, a big van if you need to carry large stuff (my daughter moving, my wife buying living room furniture) and a nice Class B camper moke up. Let me know if you are interested in the details.