Credit card tourer as well here. No problems in sparely populated areas like Kyushu (which is also really incredible) and Hokkaido.
In Kyushu you will always find Minshukus, in Hokkaido as well - but they're often a little bit more basic with shared bathrooms, if you don't mind. Also you'll probably end sleeping on some farm a little outside the next small city, which can be really nice.
Didn't try out Ryder Houses, but this will also give you some backup.
Started doing a blog on the trips just last year (while doing bicycle trips since 10 years), so not much is documented. But if you want, you can find some information there about Taiwan and Hokkaido.....