Resizing a dynamic macro to the window

I am trying to resize a macro to the size of the iframe in a dynamic content macro. Note that I am not just trying to resize the macro a la AP.resize(), but resize the content in the case when the iframe has a max width constraint due to the width of the page column so the content does not need to be scrolled. I have been able to make this work by getting the width of my iframe window and size accordingly, however, in some cases when the macro is slow to load due to latency the resize will happen before the iframe is resized from the initial 300px, causing my macro to size to 300 px wide. I have a couple of questions:

Is there some way to be notified when the size has stabilized. I’ve considered handling the resize event but resize occurs before my event handler is setup?

Another approach I’ve considered is to poll that the window size and resize my content when the window width is no longer 300 wide. This works OK, but I’m concerned that at some point that default might change and I find my macros no longer rendering properly. Is there a way I can assured of the initial width of my macro’s iframe or that it will always remain 300?