I was a bit confused,myself, on why Mike used the RC car to "deliver" the money with the black-light paint on it. At first I thought when the Kettlemans both came out to look at it he was going to "lead them away" for confrontation in the wilds or something but, instead, it just sort-of sat there and seemed placed there. Didn't make much sense to me on why an RC car was used when pretty much anything could have been used.
I thought the same thing at first about it moving, but then I thought that maybe he put it on the car to implicate one of the kids taking it out of the hiding place. Because if he just placed it on the ground, it might be a bit more suspicious.