I've biked it a few times - first time way back in 1987, last time a couple of years ago.
Hwy 200 out of Missoula is pretty busy - shoulders have improved greatly since '87.
Traffic gets lighter after the Seeley Lake junction.
There are some excellent places to camp in the Ovando vicinity along the Blackfoot River.
Most of these are Montana Fishing Access Sites (FAS) - some free, some with a fee.
FAS camping is low-intensity and some of the nicest to be found in the West.
I love Ovando - a friend used to be the town doctor.
Ovando has a bar, café, and general store last time I was through.
Don't recall any businesses in tiny Helmville - but you could ask for water if needed.
The road to Drummond is fine - not too steep heading south -
But a pretty fast downgrade after the summit.
Used to have a 5-mile dirt section, but was paved in 2012.
Here's the Montana DOT Bike Map: