There are plenty of universities with wind tunnels, you only need up to around 40m/sec or less, I wonder if it might be worth finding out if it would be possible to borrow/hire one for an hour or two? If you picked one where students were on automotive design courses, you might find they'd be very interested in having a look.
Tim H. 1986 4/4 VVTi Sport, 2002 LR Defender, 2022 Mini Cooper SE
