Extra propane tank; can it be hooked up to fill port in RV?

You know, the 4-gallon propane tanks sold by Lowe's? Just wondering if there is a direct-connection using the fill port for the permanent RV tank? Or does something need to be modified in order to temporarily use this additional propane in case I run out? Heading to a deserted island for 8-days of surf-fishing and don't want to run out since there are no roads, houses or stores. May have to use some heating at night, as well as frig/water heater but those don't take much fuel. Thanks in advance!