I am trying to make a telescopic tower using aluminum tubes up to 8" square .188 wall thickness. I would like 3 sections to telescope. Anybody have an idea how I could accomplish that?

You should provide some data and images of the type of application and its way of using it. A hand-operated telescopic mechanism that locks in a single final position is not the same as another whose sectors unfold synchronized with each other and driven by an actuator, which can lock at any point of its stroke.
You will see cases like the first in the attached images (a ladder, a cane, etc.). Cases like the second are, for example, those of a crane with an elescopic arm.
Knowing the type of application will allow you to know how demanding the guides of the mechanism will be. It is one thing for them to resist a basically axial load (which does not require them, as in the ladder) and another is to receive bending loads (which could lock and/or break them, as in the case of the crane).
So, you will need to define two things: a guidance system and an extend and lock system, but both will be very dependent on the application you want to give the mechanism.
Best regards,
Marcelo

I currently make a two section camera arm . I want to add another section but not sure how to do it. I took over a company that made it. Now I want to make a longer arm. Here is my website www.Telecopicjib.com