DEFINITELY use your toilet and your water. That's the entire point of having a trailer.
I remember when I bought my first trailer, a new Scamp from the factory in Minnesota, and I was pulling it home across the country. I got deathly ill in the middle of the night going across the Ozarks in the freezing rain. We were all sick...even our dog.
The best thing I have EVER purchased was that full bathroom in that Scamp. SURE came in handy that first night...and every single time I've needed it.
Carry a good amount of water and don't be afraid to drop a fragrant floozy pa-two-zy in the e-coli oven when you need to. Don't be afraid to use it.
Again...that's the point of having a self-contained RV.