Lots of FWD cars have rear struts. Early 2000's Ford Taurus is one example. Lots of semi trailer axles have a center hump / drop. Primarily used on tankers or bulk carriers to clear discharge piping. Obviously you don't need anything that heavy duty, but the concept is the same. Send me a PM some time if you want to talk about suspension design engineering. I have over 20 years working on everything from ATV's and Side-by-Sides to Semis, Motor Coaches, and Fire Trucks.
Something like a Citroen 2CV comes to mind. You could maybe do it with torsion bars and run standard tube shocks to keep the height down.
A swing arm suspension like that is not uncommon, VW, Citroen, Heavy truck auxiliary axles, Side-By-Side ATV's all have variations on the theme. The challenge is getting the forward pivot connection / bushing to resist all the degrees of freedom and yet maintain some level of compliance and not negatively impact the ride and handling. Extra links are often used to control motion and keep things positioned correctly. Here is a design I worked on back in my UTV days. Swing arm and Coil over shock. - Off Road suspension with 14 in of vertical travel at the wheel. Obviously, you can get away with a stub shaft for the axle and don't need half shafts if you go front wheel drive. Notice the swing arm Y's out in the front. This was done to help spread the torsional loads out over a larger area. I also have done work on the tag axle used by McNeilus for their Rear Loading refuse bodies. Same concept, swing arm, stub shafts for axles, and air suspended. Be aware, roll resistance is horse shit with this type of suspension. You will need an anti sway bar of some sort or the other. The side-by-side shown above has one, but it is hidden in the images. The refuse truck got away with out an anti-sway bar since the main tandem drive suspension handles those duties.
That Citroen has hydro suspension. That's what you are seeing. As @FrozenMerc shows, no need for central connection between the 2 sides. How much travel are you planning on. A LSR car doesn't need much, and at high speeds, balance and aero can be more challenging. Is it a street car with low drag? That's going to be a different can of worms with normal travel causing changes to the aero underneath. Most all supercars have undertrays now.
My TR6 didn’t have a rear sway bar but handled beautifully. I had a GT6 that handled even better and it didn’t have a sway bar either. The GT6 had lower wishbones and the upper end was located by a transverse leaf spring.
A couple thoughts if you want an aero body, I'd suggest standing on the shoulders of giants (of industry, who have deep pockets and wind tunnels) and look at something like the EV1. https://www.carfolio.com/search/specific/?searchon=cdb&asp=&y1=&y2=&num=100 Then, remember the myth busters where they tried the golf ball divots? It was proven. Combine those. As for the tunnel, it's going to have to clear normal road use, so that drastically reduces ground effect. If F1 and Indy cars can use airfoil tubing, so can you.
The Vega exposed me to Kamm, being called the Kammback. https://en.wikipedia.org/wiki/Kammback It requires fine tuning, like all aero stuff, but it sure looks more practical for a street car people have to deal with. No long tail unseen by driver, no long reach to get items in and out of the back. We all like a long swoopy tail, but it's place is on the concours grass, not city traffic, IMHO, even with modern cameras.
Sorry, just thinking and offering another possible choice. As for traffic, because one of these fine upstanding people following you wouldn't keep a safe distance and ride right up your backside.
When I pull my trailer empty, I keep a close eye on the rear view. Let's just say I've seen the general public, and I'm scared! If it isn't another SUV blocking out all forward vision, some just don't see it. I've pumped the brakes (flashing lights) more than once to avoid being rear ended. I'm just tossing thoughts out, and it seemed you didn't take the last one well. My mistake. Written VS spoken and all that.
My first thought is what about adapting a trailer torsion axle? Simple mounting, just need to figure out a way to mount a shock, or not? Rubber torsion spring, not a huge suspension travel. But at least most of the engineering is done for the loads of a trailer, which choosing the right one could be close to what you need for a car back end?
My VW dune buggy has trailing arms that seem to work well. Just a torsion bar and pair of shocks. Pretty easy to source too.
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