sits about stock level, I think. The stack jacks slip under with a couple inches to spare. I suppose if your trailer is super low there might be an issue. You could buy some at Wal-Mart and check them, I guess. Wait, why don't I go measure one of mine? I'll do that and report back.
[Edited to add: Mine are about 10" high when they are unextended. I don't know what brand mine are, but they are probably similar enough for you to get the basic idea about whether or not they would work. If they are close, or a site has weird angles, you could back the tires
up onto planks to get more space.
I say that they are probably going to be similar because I have 2 each of different brands and they are pretty close to the same. I do have to tilt mine to get them under the body "skirt," but they are fine once I get them under there. That said, there is not tons of extra room.)
I use mine for stabilizing (they wouldn't "jack" if you tried, although they are commonly called "stack jacks"), but I don't always put them at the very ends of the trailer. In fact, I usually put the forward ones as far back as I can get them on the widening part of the triangle (not all that far back as there are gussets that I run into); the rear ones I typically put 2'-3' feet forward from the back of the trailer --- where the weight
will be on the bed inside. That varies slightly with the terrain.
The way I deploy them, there is no "pressure" when spinning them up into position:
1) Back trailer in place and get it level side to side (I back onto squares of wood).
2) Make trailer level fore-and-aft with built in central front jack (the "wheel" or whatever you have), but then drop the nose back down slightly.
3) Place stack jacks under frame in rear and spin them up hand tight or slightly loose (depending on how you did #2).
4) Raise trailer again slightly with nose wheel so that rear jacks become tight (but not overly tight).
5) Place front jacks under front two sides of frame and spin up tight (they have little pins in the spinners that give you plenty of leverage).
I'll post back after I measure mine.
PS: Steps #2 and #4 are probably un-necessary. It's just the way the former owner showed me that they did it, and so I continued; but I'm sure you could just tighten all four by hand, since that works perfectly well for the front ones.