I think we will start seeing more ads on TV after Labor Day which is the traditional start of the political schedule. I'm actually thankful that the advertisements have not appeared, lest we burned out by Election Day.
I'm not certain that advertising on billboards is that effective. The messages on them will have to be about the same length as a bumper sticker because most people won't be able to take their eyes off of driving. As someone else mentioned on DU, there are some billboard owners in the rural counties that won't even accept business from Democratic candidates.
Beto has also snagged some media appearances on cable news (particularly MSNBC) and the late night talk shows. At this stage of the campaign, it may be a wiser use of resources to defer to those appearances and go on his 49 day tour around the state so that he will have more to spend on his campaign in September and October. Those appearances in small towns do get attention in the local newspapers and I try to post those articles when I see them.