Long time have passed, but I still carry this crazy idea around, and it have evolved slowly so I felt like sharing my ideas now:
I still love the Saab classics 96 and 95 from the 1960's and what's new since my last post is that I have got two Saab 95 station wagons and an old scrappy trailer to experiment with. I intend to modify the trailer so heavily inly a steel tube or two will remain, but it's a much cheaper way through bureaucracy and regulations to get a street legal DIY trailer.
I plan to use the entire front suspension and transmission from another Saab 95/96 and attach it to a telescopic towbar (poor english?) so I can change the wheel base between the car's rear axle and the trailer's wheels. The retracted position is the normal driving mode where the trailer is firmly attached to a pair of higher mounting points that makes the entire structure rigid to act as a whole six-wheel car. The extended position is simply what's needed to make the trailer street legal. -I must be able to drive the trailer in the usual manner with the hitch-ball as the only mechanical connection to the car, but it's allowed to have a retractable towbar to make parking and storage more compact. (so "oops, i forgot to extend the towbar before driving away, sorry!")
The little Kubota 600cc two-cylinder diesel is still en engine I want to use in the trailer, with a V-belt connection to the Saab gearbox permanently mounted on the trailer frame and driveshafts. -Nothing prevents me from building a street-legal trailer with driveshafts and gearbox, but the engine will be mounted later as "payload".
To improve aerodynamics the roofline of the Saab 95 may be slightly modified in the rear, and the windshield can be replaced by a Saab 96 rear window turned 90 degrees for a better fit. This looks really good with the Ecomodder aerodynamic template! The trailer will have an aerodynamic body shell that when retracted fits perfectly to the rear of the car. (this will off course look silly in the extended position...)
Since the trailer will be quite light and is not intended for carrying extra cargo it can have soft suspension to barely carry it's own weight. I guess progressiv suspension like air bellows may be a good choise since there will probably be some heavy forces to handle while driving up and down ramps/slopes and over bumps. The attachment points to the car must be rigid as well. (I don't intend to go offroad driving with this machine, even if it will practically be a 4x4, or rather a 4x6...)
If I make the aerodynamic shell lightweight and removable I can put it on hinges and flip it upwards while parking with the trailer attached in the retracted position to save some valuable space in lenght.
If I use the front suspension of another old Saab it's possible to have a low-speed mode where the trailer wheels can steer freely, and be locked in straight position at higher speeds. I guess the entire six-wheeler will be very stable at the highway this way and still be easy to turn without sliding in city traffic. (while reversing with the trailer, it's wheels must either be locked straight or steered by an electric motor, or else they will quickly steer to full stop in either direction)
So, what do you think? How crazy am I?