CRM 2013: Iframe does not display the url set in onform load event with setSrc. How to make this work?

Question

I have a situation we need to display a url in Iframe when a form is loading. the url is set in code with setSrc, or updated the query string value. this worked in crm 2004 not any more in 2013.  MSDN states the below to avoid in OnLoad event. what
is the best way to handle this situation?  Searched web people recommend using setInterval which i dont want to use.
Any help on this issue is appreciated. 
https://msdn.microsoft.com/en-us/library/gg328034(v=crm.6).aspx
Avoid using the OnLoad Event. IFRAMES and web resources load asynchronously and the frame may not have finished loading before the Onload event script finishes. This can cause the src property of the IFRAME or web resource
you have changed to be overwritten by the default value of the IFRAME or web resource URL property.

Answer 1

Thank you for you reply.  this URL you send uses window.setInterval which i am not comfortable using it. we need to call clearInterval(),
if not the IFrame refresh every second. 
function SetURL()
if(Xrm.Page.ui.controls.get("IFRAME_ActivitySmmary")!=null)
Xrm.Page.ui.controls.get("IFRAME_ActivitySmmary").setSrc(reportUrl + "&id="+ customerId);
                Xrm.Page.ui.controls.get("IFRAME_ActivitySmmary").setVisible(true);
else
{ window.setInterval("SetURL()",1000);}