Backpacking Hokkaido easy to camp?

Destination: Japan, Hokkaido, 1 month (from mid July) (North-West Hokkaido as a starting point) Have the air ticket already. huraaa!

Main concern cheap accomodation ... just everywhere in Hokkaido.
Big cities (Sapporo) no problem: Internet cafe ,...

1) Is it easy to ''put a tent'' for the night in areas not designated as campsite? Parks in towns? Just out of villages (asking permission first) etc.?

2) They are Sento (communal bath houses)
in Hokkaido that can be used as basic overnight accomodation? (like jinjibang in Korea)
What about camping accomodation close to Onsen's or Onsen's open 24h? (I went to Japan once but I'm not yet familiar with Onsen's)


Transportation:
public transportation: e.g. (Seishun Juhachi (18) Kippu) and occasionally hitchiking.
I will NOT use a motorbike or bicycle just public transportation and walking.

For sleeping: I will carry sleeping bag and tent. Will try to find a Riders home if close
to transportation.

Time is not a problem.
I'm not interested to see Hokkaido highlights
only. Meet Japanese people, make friends, enjoy Hokkaido landscape...

Is it easy to ''put a tent'' for the night in areas not designated as campsite? Parks in towns? Just out of villages (asking permission first) etc.?

Camping outside of designated camp grounds is illegal in many parts of Japan. In some parts it is legal to camp in public spaces, but often it is not obvious whether a park is publicly or privately owned. So out of respect towards your host country, I recommend not to camp outside of camp grounds unless you are sure that it is allowed. I am not sure about the specific situation in Hokkaido.