Sleeping pod micro boat

Have you studied any specific designs from Matt Layden that you like? Which features are most appealing?

 

I ran across an ice fishing sled that might be close to what you're looking for: Eskape 2800 https://geteskimo.com/products/eskape-2800 Sled is 70" long, so just a bit short of your 78" criteria, and the sled probably wouldn't be particularly sea worthy on soft water, but the concept of the tent that folds into the sled might be valid for what you're looking for. It'd be a matter of mounting a similar type tent/frame on some sort of dinghy/canoe

I use a smaller similar sled lashed to an old bike trailer for hauling my camping gear when there isn't enough snow for the sled. An old bike trailer for carrying kids could provide a ready, cheap and light way to add wheels to the type of craft you're envisioning. My trailer hauls 100+ lbs without issue. Like a solo canoe with a sleeping pad in it, and some sort of cover/deck. Possibly 2 solo canoes, with the top one cut in half so you can slide it open in the middle, and then slide it shut when needed, or hinged so you could have a little catamaran on the water, but a capsule for sleeping at night. Should be able to manage that under 100lbs, so rather portable, although the length might stick out the back of a pickup, but not so far as to be impossible.

Your post made me remember this project, which is cool on many levels: Building the Microship Trimaran - Nomadic Research Labs https://microship.com/the-microship-substrate/ He is using a small trimaran, that he added wheels to make amphibious.

 

Do an image search foamy bike trailers.
If Silvertooth is right, some of these might be OK.
This Vespa teardrop trailer made of foam, incorporates a functional kitchen and space to sleep the rider - Yanko Design https://www.yankodesign.com/2023/01/28/this-vespa-teardrop-trailer-made-of-foam-incorporates-a-functional-kitchen-and-space-to-sleep-the-rider/
#5 looks too wide, but this is a boat forum.