A makeshift cap might work on the inside of that flange as well. Do keep in mind though, on the fronts the end of the axle is what it is. A caliper helps immensely, to measure the inside and outside diameter. Too, google something like: black rubber end caps round
The original 17” wheels only come with hubcaps, and no center caps, right? Does Toyota consider that protection enough?
The gen5 lower trims(LE/SE) have wheel covers and no caps over the hubs. Toyota must think the wheel cover protects the hub enough. And they're probably correct. You're going to get some light surface rust, but nothing serious. I think I'm going to spray some Fluid Film on my hubs when I swap to winter tires in a week or so, and that might even be enough if I was running steelies with exposed hubs. If I was running steels with my winter tires in a region that uses salt, I'd definitely do a Fluid Film spray at the very least. If you run a stock 17" wheel without the wheel cover, you might be able to use a standard Toyota hub cover. I thought the wheel hub size for the 17" wheel was the same as the 19" wheel that comes with hub covers, but I seem to remember an owner having problems in that area, so I might be incorrect. Maybe take an inside diameter measurement after you get your LE and one of us can do a comparison with our XLE/XSE/LTD. But I'm pretty sure those OEM caps won't work on a steelie wheel like the one that was shown on the previous page.