Very interesting. it sounds like we have very similar requirements - i too want a cab-over bed that can mount on a smaller truck such as a european-spec ford ranger super cab or nissan navara king cab, and I would prefer to go frameless if possible.
XPCamper has expanded into Europe and our V2 hard sided popup is available to view in the UK, and buy across Europe. It is a clamshell design where each half is a 35mm thick fibreglass foam sandwich, laid up in a female mould with bi-direction glass. When the two composite interior mouldings are bonded in you end up with an incredibly strong, stiff, and impact resistant shell. Because it is moulded it does not have weak points like a bonded composite panel camper would; or cold bridging and condensation issues like an aluminium framed composite camper would.
We are building custom trays with a cutaway design, four storage boxes and a 5ft drawer. They will be as light or lighter than the tub on the standard truck, but of course be much more practical. These trays are designed and built to match the styling of the parent vehicle; either a single cab or king cab variant of:
Toyota Landcruiser 79 Series
The camper lifts off with jacks in 10 minutes. Leaving a flatbed base with 4 receiver sockets. Into these receivers you can fit drop sides, a custom canopy, or any other structure that you would like.
We have partnered with Arctic Trucks to build a demo vehicle using an Isuzu D-Max AT35 extended cab (see my avatar). This is an attractive option because the 35" tyres, suspension and other goodies are all covered by the OEM 5 year 125,000 mile warranty, and dealer finance. We can also build Navara and Hilux AT35s with the same OEM benefits.
Sadly building moulds is an expensive business for a one off camper. But can be economic if used multiple times. Hence we are able to offer completed camper and flatbed packages for a similar price to what it would cost you to build one yourself. You benefit by not having to do the labour, or spend ten years evolving the build process as we have. What you end up with is two yacht hulls: We've all seen those 50 year old neglected fibreglass yachts in marinas yet they are still floating unlike a similarly neglected wooden or aluminium yacht. Consequently an XPCamper has a residual value considerably higher than a homebuilt camper if you decide to head in a different direction. More details on our European website - see my profile for the link. If you need to sleep four people, rather than three, then probably best to give me a call ;-)