gps for rv's

[msman]

hey all

just wondering if on your travels anyone has come across a gps which is suitable for rv's/trucks i.e. one which avoids low bridges and weight limtied roads.
an elderly lady i work with is retiring soon and is going on a around australia trip in a rather high rv and asked me today if a gps is available for this purpose.

i have seen a binetone carrera with this feature but they offer poor reliability.

cheers