The frame and shells on any of the FBRVs don't add up to much weight
. It's the ammentiies and stuff you bring along that push the scales up.
Just for info -- my parents when they were still living pulled a 13 ft Scamp
all over the nation with a Renault R10 fuelled by propane
during the gas "crisis" of the mid 70's and early 80's. The Renault was supplanted by a Mazda pickup during that time.
Later they upgraded through a series of larger and larger rigs then dropped down to a 16 ft Scamp
that they pulled with a 6 cyl Toyota Cresida.
Dad always said the Scamp and the Mazda pickup, which was a 4 cyl was his favorite traveling rig.
So I think most any 6 cyl rig would pull a small FGRV just fine.