Hi Involute, for your second part:

> On a possibly related note (related to the initial question of this thread), I'd like to make a tunnel
> between the two rectangles in LoftProblem.jpg (below), on the top and bottom of the plate they're
> on, but when I loft between them there's no opening created <....>

That's because Loft does not make openings, it makes surfaces or solids. To make an opening you'll need to use boolean difference after doing the loft.

Select your main object by itself first then run boolean difference then the tricky part is to select the lofted solid as the cutting object.

There are a couple of different ways to do that, you can do it with a click if you get the click right on a zone where the loft happens to be showing over top of the main object, or a couple of less finicky ways are to use Window select (click in empty space and drag a rectangle, preferably starting from left and going towards the right to get a "only contained inside" selection rectangle, also it's a good idea to have deleted your rectangles after building the loft so you don't accidentally select those as well since 2D curves can also be used as cutting objects but they will cut straight through), or another thing you can do is in boolean difference when it is asking you to select the cutting object you can push the Edit > Hide button right then without the command exiting and it will hide the main object so you can more easily see and click on the lofted result.

Also with the window selection method if there is not any good empty spot to click on to begin the window drag you can hold down shift+ctrl when you click that will force a selection window to happen right away.

Let me know if any of this is unclear and I can make a demo video.

- Michael