Yes if you create the RTC report using “Create Layout Suggestion” then it’s important to remember that its only a “Layout Suggestion” and that the suggestion typically is not direct usable unless your classic report is very simple. Otherwise then it’s really a pain to do.
Did you read my blog post about this? Microsoft Dynamics NAV 2009 Upgrades and the RTC Reporting Nightmare
That is currently the only way, expect to use 8-20 hours to “upgrade” an classic Invoice report to RTC. After you have done it a few times, then maybe it will take you less. But it’s not easy to get a nice looking result.