I just read a post about how voting machines in Ohio are going on sleepovers before elections. Whether they’re being protected or hacked is up to you, but clearly physical access to voting machines is considered to be an influence on their validity.
How about this: Put them all in a large group in a parking lot. Then put some simple barrier – maybe police line tape – around them. Then alert media, activist groups, and everyone else that they are there. I’m guessing you’ll end up with enough witnesses and video that any attempt at tampering will end up on tape from several angles. Problem solved. For free, and to everyone’s satisfaction.