What about the Expeditionarry? from the wooden boat competition. Seems like it could fit the bill, designed with folding beams, but from the weights quoted on the site I would think that a demountable version would be easy-ish to assemble then sail. Especially if built in a few bolt together sections.
The options section towards the bottom of the article mentions that the ww hull can be scaled up to 150% which could make it an interesting option for a minimal coastal cruiser. Less minimal than your sidecar, but I would think a more straight forward build than a Harry or EX40.
Not sure if the design-work is complete but from the Bucket List options section "Bucket List can also be supplied with shorter beams and a larger windward hull, containing 2 double bunks, headroom, galley and a cockpit for 4. This would be suitable for longer races or cruising"
I do realize that Bucket List has evolved from the renderings shown on the HP site, but obviously Rob put some work into that stage of the design so I would imagine that those drawings are still floating around on a hard drive..
Seems like a combo of those two designs would make for a great lightweight, relatively easily transportable design. I know that my wife and I would be interested in a design like that.. In-between El Camper and Harry/Ex40.