yes, I agree with the above – it’s pretty risky given the information you have posted – and especially standing up – I did once in an emergency take my concert grand to a wedding in a convertible with the top down leaning up against the back seat, but I was a nervous wreck the whole time – and the wind made the cover flap against the harp pretty violently if we went too fast –
If you have no friends who have vans I would suggest that you hire a taxi that is wheelchair accessible – you need to call your local taxi companies to find one – or an 8passenger taxi and have them put the seats down – either way you have the harp enclosed in a vehicle with appropriate climate control – but do check it out in advance to be sure that you can fit your harp in the particular vehicle they send –
You said this is an audition – I assume for a job – so if you get a regular job, what are your plans for moving your harp on a regular basis –