Whenever we cook (which is twice a day), we have to open the windows and the door in order to get enough air – otherwise, the propane/carbon monoxide alarm goes off. In warm, dry weather, that's no problem – we just open the front door all the way, we step outside, and we latch it open. But in cold or wet weather, I would prefer not to have to go outside, and we often don't want the door open all the way. But there is no latch for holding the door open halfway.
So I came up with a rather simple "Mickey Mouse" solution. I mounted very strong magnets on either side of a short strip of flexible steel. One magnet attaches to the bolt assembly on the door, and the other magnet attaches to the strike plate. Here's what it looks like when deployed:
The magnets are neodymium or rare earth magnets, salvaged from old computer hard drives. (I have a friend in the computer business, but I would bet that you can get these things from any local computer repair shop.) The magnets have holes in the mounting brackets; using a drill press and some care, it is possible to enlarge the holes to accommodate very small machine screws.
I used a mallet to flatten out a 1 foot strip of galvanized roof flashing. I then drilled holes for the magnets and put them on either side of the steel strip:
Note that on one side, I mounted a small piece of wood, just to keep the strip of steel from flexing too much.
I then added an extra piece of perforated steel to the inside of the door frame, above the existing bolt assembly -- this is to provide more surface area for the magnet to grab onto:
It was necessary to use a flexible steel strip, rather than something more substantial, because the bolt assembly on the doorframe and the strike plate are not exactly in the same plane. So each end of the steel strip flexes slightly, to accommodate this minor disparity:
The whole thing can be deployed from inside the trailer: I open the little hatch in the screen door next to the latch. I stick the far end of the holder out onto the bolt assembly. I then attach the near end of the holder onto the strike plate. Here is what it looks like from the inside:
These killer magnets seem to be strong enough to hold the door in place, even in a fairly good wind. But I haven't field-tested this yet, so we will see how it does in the typical strong afternoon Sierra breeze.
Finally, for storage, I screwed a small piece of perforated steel on the inside wall of the trailer, next to the front door frame. The magnet sticks firmly onto that little piece of steel.