So, am cleaning out things and have found a hole in the back that as far as I know should have a rubber plug. Lots of dirt around it (inside vehicle) and while it is dry now, some evidence of some moisture at some past time. I was going to spread silicone all over it. Then I thought I would just duct tape over it. Then I thought duct tape covered by silicone would be easier to take off if I ever needed to. Then, I got the bright idea that I have lots of "corks" of various sizes. One fits. I would shave down the "head" a bit so it it not sticking up much, but that should work, right? I am sure I can get a plug at Toyota. And it might even be less than $5, but the 80 mile drive is a bit of a killer.
Red car or white? Cork it and wait until you have to go to the dealership for something else to buy the $5 plug. Corks last for centuries in wine bottles (presuming that they're properly stored) and I don't think that the rain and dust will know the difference for a few months (or years) until you make it back into civilization. I presume that eventually the cork will dry out and shrink, but properly applied it's more than an adequate fix for your car. I also like the Duct-tape approach but the cork has more panache. Good Luck!