Sandy,
I have used one of these to load 12x20 holders. It is "do-able" but certainly quite cumbersome. I found that one holder at a time was quicker (including the time penalty to close the box and swap holders) than trying to stack and swap multiples. This however was based on a modest smount of practice, one might find that more effort lead to a different conclusion.
Unloading:
1) box, post-its and holder into tent box on top, 2)take the first third off the box and stack so that "two tops" cover the inner most box with the inner box towards the bottom, 3)swap box to bottom 4)crack back the top DS and remove film by looping 180 towards the lightlock end of holder, 5)apply post-it to back of sheet and slide, crack box lids open and slide sheet of film under stack in box, 6)flip and repeat.
Loading is essentially the reverse, the film is made manageble by curling it 180 and feeding back into the holder (saves space). Not attempting to reverse the darkslide makes this much easier. (the wings I assume solve this problem) I would certainly never advocate not reversing the slide but when you have only two holders and lots of post-its (and not much sense) it sometimes seems like wonderful idea. FWIW you might call the nice lady at Camera Essentials (Patty Harrison) and ask her if they could modify your tent. I have found them to be very nice folks.
Celac.