I have a couple of rig shots (i.e., camera attached to long pole hanging off of car or other moving object) in mind that I'd like to try, but don't really want to go to the expense of buying the kit to build the rig since I only intend to use it a few times.
What kind of vehicle? if car do you have a sun roof? Are you doing this on a higway at 70 MPH or on a side road at 25- 45 MPH?
PVC my not be the strongest- you can go to Lowe's and get steel pipes fairly cheap. I would try to use sheet metal to fabricate a box to place the camera in and attach both to the steel pipe. You would be able to get a bolt that will fit the tripod mount.
Sheet metal can bend with a strong arm. It would protect the camera from wind and anything that flies through
the air.
This may cost some money and time - but I think it wouldn't be too much. This may be a fun project...