I've "flown" out of BPT a couple times, and by that I used to utilize the United BPT-IAH bus, because once a upon a time it was a great way to get lower fares out of IAH. One time I left my car for a whole week, another time it was for 4 days. Both times I didn't have any issues, just use common parking sense and don't have any valuables (or preferably anything visible).

If you're concerned you can park closer to the terminal where more people are likely to be milling about. It's a surface parking lot that is right in front of the terminal.