If the 4th gen is like the 3rd and other models, there's a drip tray under the edges of the sunroof and drains at the front. Any bit of water that comes past the sunroof should drain.
Be sure to add checking the sunroof drains to your periodic maintenance - once a year or so open the sunroof...
Agreed, at 7.5% there's not a lot of investments to compare which don't have substantial risk.
Presently Southeast Toyota is offering 2.99% at 36 month, and my credit union offers 4.45% at 48 month. Those have more options for better rates in conservative investments.
As for personal debt...
Depends on whether you can make more by investing the cash than you'd pay on a loan.
Specifics will vary by individual risk tolerance, credit score, and available financing promotions. Don't spend more than you can afford, and choose which works best to your individual situation.