The Grundy County coroner said the fire broke out at about 3 a.m. in the parking lot of the Loves Travel Center right off Interstate 80 in Morris.
Morris firefighters found the RV fully engulfed in flames. It is not clear what caused the RV to catch fire.
The two victims were pronounced dead on the scene just after 3:45 a.m. An autopsy was scheduled for Friday.
They were later identified by the coroner as William S. Davis, 52, and Chelsi A. Bates, 31. They were both from Mena, Arkansas.
The coroner and the Office of the State Fire Marshal are investigating the fire. Further information was not immediately available.