CORRECTION: The current Squall, IN FACT, appears to have some sort of door, so I guess (OOPS!) that example is at least out of date . But it appears that certain earlier Squall versions may have not had a door. (??)

MSR Wings and Golite Lair would be more accurate and current examples. But it may be that my entire point is going out of date. Looking around, I see, or at least imagine I see, fewer doorless tarp shelters on the market now than some years ago when I acquired the Batwing (in which, by the way, I've spent many pleasant and mostly rainless summer nights).

here is a fantastic site for using simple tarps with a couple of options for complete coverage:

http://www.equipped.com/tarp-shelters.htm

There were several pyramidal configurations that I used with simple rectangular tarp that afforded a door of sorts. The simplest entailed tucking a sizable corner of tarp underneath shelter.

This in effect lopped off a triangluar piece of the tarp, constricted size of shelter and subjected it to abrasion. But it was pretty effective somehow. I can no longer quite visualize method, or how or why it worked, but for a long while, I had it nailed pretty well, even though it was a somewhat fussy procedure. I think the 9x10 tarp used this way provided a largish one-person-type space of maybe 25 -30 square feet.

The resulting "door" functioned something like SilShelter's door, in that it relied on stakes (or slinged rocks or small logs -- much easier to move and adjust for opening & closing..)