An old thread, but as another thread drifted into this topic, I thought I would repost my comments and answer a question here.
A 'true' tonneau cover would be nice, but I don't see how it could be successfully secured for high-speed driving. My XK120 and 150 had tonneau's and they worked quite well (no inside flapping that I can remember). When I was dating my Lady-to-be, we were driving from Boulder to Denver in the XK150 with the top down. It started to snow and my Lady started to complain that she was getting cold. Not a problem, pulled over and quickly put up the passenger side tonneau and she laid under it. A plus was the heat from the heater actually could be felt (I always tell people that an XK heater only kept itself warm). Please note that the top on XK150 was a cleverly designed piece meant to frustrate any driver in a hurry to put it up.
The Jags used a combination of treaded studs and flat snaps to secure the cover. Magnets would be tricky as no guarantee that they would hold at speed. Making the tonneau to fit over the head rests isn't that big of a challenge (the driver's side in the XKs was fitted for the steering wheel), but would increase cost over a flat tonneau.
In the tonneau thread that was linked into this thread, the slope is important. If the dash is lower than the body behind the seats, that is a problem with water flow. Note that any tonneau would need to be removed before the top could be raised (nothing new as it was the same with the Jags).
In all, I do miss having a tonneau. I have parked La Bęte leaving the top down but had to remove leaves and other bric-ŕ-brac afterwards. That is something you don't do if you have a tonneau. Chances of intermediate light sprinkles/showers are handled with a tonneau. As also pointed out in the other thread, the speed/ease of putting the top up does mitigate the need for a tonneau. I do think about the wear-n-tear on the top system given the number of times I operate the top (daily on most days in spring and fall, less in summer and winter).
I do feel a tonneau looks sharp on a sports car. It is what I grew up with and no OTS was complete without one. In my eyes, La Bęte looks a bit naked without one.
Padgett responded with:
Did you have a drophead ? I had a 150s roadster and as I recall the top just pulled out and up from behind the seats, not like the erector set in my MGA. Do agree the heater made it "less cold".
The tonneau cover had snaps and a zipper but suspect Velcro could work as well. Since it extended under the base of the windshield it did not get much wind even "at speed".
I had an OTS. Remember, to raise the top you had to:
-release the arms holding the tonneau extension to fold it back towards the boot, swing the top out from behind the seats, then engage the bar sewn into the bottom edge of the top into the two hooks that were in-front of the boot lid.
-The left and right supports that the top swung on were hinged and very loose and you needed to make sure the hinges were pressed back. When pressure was applied straight down and the top pulled forward, they needed to lock back instead of collapsing forward.
-A good top was very tight and this was the tricky part. You needed to keep tension on the top so the support hinges would stay locked back. You had to press the top forward and down to get the two locks on the front of the top aligned in the holes in the windscreen.
-The locks were bayonet style (on the top) and hole in the windscreen had the bar set inside that the slot in the bayonet had to align before it could be closed. The slot acted as cam and you had to keep pressing to allow the bayonet to rotate on the bar to engage the closed position. Best was pressing with one hand on the center of front edge of the top as the other hand maneuvered the nearside lock into the hole.
-As the front of the top could (and did) move left and right and the tension created resistance to closing all the way, you had to maneuver the lock into alignment as you pressed down on the top. If you could get the first lever to rotate and close the lock, then you just nipped over to the other side and had to press that lock into place (there was some tension and wiggle movement in the top) and rotate the second lever.
In all, some arm strength and arm length was handy. My Lady found it a challenge to do the multiple tasks simultaneously. One reason she never liked to drive the Jags.
The top on the DHC was much simpler. The top frame was significantly more rigid, had springs to assist opening and closing, was already attached at the back to the body. All you needed to do was pull the front of the top up and forward. The locks were toggle style (like on a suitcase), so all you needed to do was get the paw (it didn't use a ring) onto the hook and then lever the lock (and the top with it) closed. The DHC had three locks, so you did the center lock first (easier to align). I could close a DHC top while sitting in the driver's seat with one hand/arm.
You had to be out of the car to close an OTS top. Two people made it easier.
The OTS had a tonneau. The DHC did not. The DHC did have a fitted cover that went over the top when stowed in the down position.
I used the tonneau on my XK120 and 150 a lot. I feel it would be very handy on an SLK but not really all that necessary given the power top.
Still, I would love to have one.