It's a lot of tinkering to get right.
Create a repository on git hub and clone it to your local drive. Create a new project in rStudio.
Use the new post addin to create a post, the serve site addin to create all the subsidiary folders and the console blogdown::hugo_build() command to populate the public folder.
Your gitpages folder can be named anything, but you get only one github address. The workaround is to have an index.html in your github root that points to your different hugo site directories or redirects to a single one.
For example https://technocrat.github.io/ and https://technocrat.github.io/_book lead to the same page.
For blogdown, I followed Yuhui's suggestion and worked with deployment via netify.com to rbind.io.