I've found more than 50, ranging from documentaries to zombie apocalypse; the RV vs zombie thing seems to be really popular with 21st century Hollywood. Most of them I've watched:
What's Buzzin Cousin (1943)
From Dusk 'til Dawn (1996)
RV (2006)
About Schmidt (2002)
The Long, Long Trailer (1953)
My Girl (1991)
Love and Pain ... (1973)
Into the Wild (2007)
We're the Millers (2013)
Lost in America (1985)
What Alice Found (2003)
The Last Man (2000)
The Van (1977)
Refuge (2010)
Sightseers (2012)
American Nomads (2011)
Beethoven's 3rd (2000)
The Blues Brothers (1980)
Borat: Cultural Learnings ... (2006)
Campfire Tales (1997)
Child of Grace (2014)
Crows Nest (2012)
Darius Goes West (2007)
Dead and Breakfast (2004)
Dear Mr President (2006)
The Devil's Ground (2009)
Dusk (2015)
Escape to Witch Mountain (1975)
A Finished Life (2008)
Grandma's Blessings (2013)
Hollywood to Dollywood (2011)
The Houses October Built (2014)
How's Your News (1999)
The Incredibles (2004)
Independence Day (1996)
Jack Be Nimble (2008)
Judgement Night (1993)
Lake Dead (2007)
Meet the Fockers (2004)
Meet the Parents (2000)
Our Time (2009)
Paul (2011)
Race with the Devil (1975)
Spaceballs (1987)
Stripes (1981)
The Wild Thornberrys (TV series)
Winnebago Man (2009)
World War Z (2013)
2012 (2009)
Slither (1973)
Barefoot (2014)
Diary of the Dead (2007)
A Good Funeral (2009)
As I find more, I keep up a list on IMDB. This discussion added thirteen titles I had missed, or had not thought of as RV movies.