Jeremy,
You're right, being next to the metal of the RV is the
problem. The solution is just exactly what you probably
think it is, move it away from the RV. The "how" is the
hard part, there really isn't a 'good' way of doing it
that doesn't envolve either a lot of effort, or money.
Tilting the antenna may make some very small improvement
but don't count on it. The idea is to get it away from
the RV as far as possible, or above it as Cecil said. If
you could raise it far enough to get the exposed coil and
whip above the roof line, performance would be much better.
If the whip isn't very 'whippy'/flexible, I think I'd see
if I could find one that is. It will increase the
survivability of the antenna some. By the way, you would
then have an antenna and 'BCI', "Bridge Clearance Indicator".
Good luck...
'Doc

PS - You will also need to brace/guy the antenna. Plastic
of plexiglass brace works just fine.