All of the information about brooding chicks this way can be found at this link, including how Mama Heating Pad and the "cave" go together. There are videos, lots of photographs, and a lot of give-and-take with people who have jumped on the positives of raising them like this and made modifications to fit their situations.
https://www.backyardchickens.com/t/956958/mama-heating-pad-in-the-brooder-picture-heavy-update
You won't be sorry, I promise! Well, there are two drawbacks though. You need a slightly larger brooder to accommodate the additional space Mama Heating Pad takes up, and two - well, the chicks grow so well and so fast that one day you look at them and realize you don't have any babies anymore, and you just have to get more and do it all over again!