I can get my winter cover and all its supports into the trunk of my old Saab. That wasn't always the case.
I use a 30X20 white poly tarp. The white tarp lets a lot of light in. I shock cord all grommets. I use pipe insulation on hard spots. The ridge is a piece of 1/4" Amsteel that runs from the bow chain plate, over the end of one of my spreaders that sits just aft of the anchor locker hatch (both spreaders are off the mast and the mast is on a rack off the boat). The spreaders are "mounted to 6x6 with a 2x8 base using pipe clamps. The other spreader is centered at the stern rail. I have a strong,4 bolt,well backed, pad eye on the cockpit coaming, centered. It provides the purchase for the back stay adjuster. A third support is a piece of 1" sch. 40 aluminum pipe with a pvc T sitting on it that is aft of the mast step. It is also supported by a 6x6. The Amsteel runs through the T, back over the end of the other spreader, through the pad eye and to a sheet winch. When I tighten the Amsteel using the winch it gets quite taught. I played with the height of the middle pipe to give me enough space in the cockpit under the tarp. This winter has been a good test and it has served just the way I had hoped. No frames, no shrink wrap. I have other boats I cover and buy shock cord by the spool. 3 pieces of 6x6, a tarp, a 40' piece of 1/4" Amsteel and a 5' section of aluminum pipe. A small bag of foam and it all goes into the trunk.