Using a matte to provide some distance between the glass and image will help but also the type of glass is important. Standard frame glass in cheap frames is just simple glass. If the image is important consider using Museum Glass or UV Denglas or, preferably, something with a UV protectant that is a lot cheaper. You can now also get quite good UV acrylic to further reduce the cost.
Heat is unlikely to play a factor, unless you set fire to your RV! Humidity may be a factor if it is paticularly bad and direct sunlight will almost certainly fade the image. UV is the worst. Some posters in store windows can be washed out in a year or less.
The type of ink used will also dictate the lifespan of the image.
If the image is particularly important then get the image scanned by a professional photographer, retouched and saved at a high resolution. Then store it using archival products (they don't have the acids and other nasties of standard boxes, envelopes, folders etc) and use the re-print in your RV. If it is less important then a home scanner does a reasonable job (make sure it is set to 300dpi or higher)
Hope that helps.