The "cheap conversion kit" is called a "trailer". Fits behind most vehicles, carries 500 lbs and up, low loading heights, ramps, self draining in inclement weather, minimal modification to vehicle, and could have a cover attached if necessary.

Requires driver's skills to back up the vehicle, which may be an obstacle for some.

That works for some, 1.) assuming one has a vehicle capable of pulling a trailer, and, 2.) more importantly, space to store the trailer in when not in use.

Many people have limited parking space. The conversion I was thinking about would be a modification of the hinge mounting points on the trunk lid (or hatchback lid) to allow quick removal and re-installation- probably a cheaper mod than buying a trailer.

It's a simple solution if the suspension components of the sedan are beefed up enough to handle an extra quarter ton (or more) on the rear axel. Most cars are not. Vehicles that are designed to carry larger loads are.

Larger, lighter weight objects like lawn mowers would not overload the rear end. Maybe the tail end of the car could be redesigned so the middle section folds down, comes out, or stays attached to the upper part of the lid so an object like a lawn mower wouldn't have to be lifted over it to get it in and out.

Simple overload springs are available for most kinds of automobile suspension systems, usually fairly inexpensive. Even the least expensive kinds can add another 1500 lbs of capacity, but one would want to add heavier-duty shocks. The ideal setup would be automatic adjusting air shocks/springs with electric pump.

Altering the bodywork to make a usable "tailgate" might compromise the integrity of the body and weaken it, so this should probably be done very carefully.

If you're comparing costs, you need to include the cost of additional wiring and a trailer hitch to the cost of a trailer.

I've seen conversion kits for sucide trunk lids, lifts up above the roof of the car. If one had the desire and time a quick release attachment system could be devised to the mounting point on the trunk lid. As for why sedans dont come that way, my guess is that the trunk lid plays a part in the body integrity and removal would reduce body rigidity and reduce the strength in crumple zones on the rearend and rear side impacts. I drive a forester wagon and it carries everything I need, including lawnmowers.

The trunk lid isn't a structural component, but the lip around the trunk opening is. Actually, if the lid would lock into a vertical position, it might not have to be removable. I don't think you could carry a refrigerator upright in your Forester. My neighbor has an Envoy with the retractable roof that can (Studebaker had that idea more than 45 years ago).I've also seen some local homemade car "conversions" with sedans or hatchbacks converted to pickups, including a Ford Festiva. The weathered 2x12 tailgate gives it that "rustic" appeal...

Lately, I've seen several Ford Festivas with the pickup modification- two of them have "soft" curtains with clear vinyl windows behind the driver seat, most have some kind of solid fiberglass or metal) partition with glass or plexiglass windows enclosing the cabin. This is apparently a useful (or cheap, anyway) conversion for some.

Google "El Camino"

'nuff said.

Anything that hits the consumers' fancy is a good idea. The springs on a car are too weak to haul much of anything, but it could be done on larger cars. The smaller cars don't have a trunk big enough to hold a full size suitcase. But the back seat could be converted into trunk space. So yes, you might be able to convert a sedan into an El Camino.

My 1996 Mazda has buttons atop the two back seats so they fold down and I can store long items in the trunk. This also lets one sleep in the car with ones legs in the trunk.