I'll usually just run rolling courses outside, and with your low mileage, I definitely wouldn't do a lot of hill repeats.

I'll occasionally use a tm and for hills, I may use anything from -3% to +10% (occasionally 15%), depending on objective. My normal hills are 10-30% (with some steeper), so if ice has me inside, I'm likely to do something I can't do outside anyway. Good starting inclines are typically in the 3-8% range.

You might check out some of the pgms on your tm - either random hills or building up then decreasing. I think those are likely to be more interesting since you can get some variety and you don't have to constantly adjust stuff. You can tweak something if it doesn't feel like what you want, and it should remember that the next time it comes to that part of pgm.