I have the same question. We've been using RTP dialog boxes for a couple of years now with no issues across devices because our website was not responsive.
However, we recently launched a mobile-friendly site and have not been able to make our dialog boxes render properly even though they are basically just images, no live text or anything fancy. I tried doing some simple CSS (width: 100%; and max-width: 650px;) and that doesn't seem to work. the image gets reduced in size, cropped vertically, and moved down and to the right on mobile devices (screenshot and preview link below).
There are "mobile" templates in the RTP library but the background image is visibly distorted as the viewfinder is changed so I'm not sure how mobile-friendly those are.
David Myers, do you have any tips for how we can get RTP dialog box images to render properly across devices?
Best Advise currently is to use the preview in the Campaign to see how the campaign will render on desktop and also use this preview URL to test it on mobile, and make sure the campaign HTML fits for all devices before going live with it.
With Mobile Responsive sites, the testing and previewing is important as all sites are built differently and react differntly. You can also add any CSS and override our dialog default settings in order for it to fit exactly your needs on the mobile site.
On a product development front, we working an easier way to preview campaigns for mobile (like you preview email for desktop mobile etc...) and also improve our templates so they work on all devices desktop and mobile respectively, currently they either for Desktops and the Mobile templates are for mobile only.