Booleen reduction

Hello everybdy

I can’t make a boolean reduction that takes only the external form of my object.

My object is a fusion of several objects. I think that if I manage to keep my external shape, but inside I have a completely full element I will be able to make my boolean reduction only of my external shape

[https://i.stack.imgur.com/rdSSx.png
https://i.stack.imgur.com/cCyFi.png

If you have any ideas I would be very grateful