I have the latest version of CS-Cart (4.3.3), and I'm currently using Simtechdev's addon (http://www.simtechdev.com/ccavenue-payment-gateway.html) for the integration of the payment gateway within CS-Cart. However, even though now CS-Cart has a one-page checkout process, it is not attractive, and I want to utilize the iframe integration functionality of the CCAvenue payment gateway. Basically, the checkout process should be in one-page, instead of being redirected to the separate payment gateway page. You don't have to entirely develop a new addon for this. Just do the iframe integration.