Probably not enough data to suggest a trend but interesting nevertheless:
According to data provided by Harris County Clerk Stan Stanart's office the total Republican early vote numbers are as follows:
8,231 - In person voters
14,750 - Mail-in ballots returned (25,007 sent out)
1,537 - In person voters
6,621 - Mail-in ballots returned (13,458 sent out)
If these numbers hold this is going to be a VERY low turn-out election.
However, I would expect these numbers to pick up as the week goes on, but I'm unsure of how far they can realistically be expected to increase given the low voter attention being paid to this election.