Thanks both. " looks like dried up rusty water " Sorry, no, it is my carelessness in not vacuuming the dry brown dust before taking the photo. The boot (trunk) feels dry.
I will take your advice. I have a 14 year old son who likes being shut in the boot for some reason, so he can help with the hose test.
I have used brushes and a powerful vacuum to remove the surface white mould but it has eaten into the fabric and so has not gone back to black.
I am now using forced ventilation with a greenhouse hot air blower to thoroughly dry the deep boot, but it does not feel damp. I suspect that I will never get rid of the spores and the mould will grow again.
Yes the seal does look wonky. I will try to re-seat it.
The boot has a tendency not to fully close unless you press it shut. This has happened a couple of times but, as I say, the interior feels dry.
Regarding design, if you want to grow mushrooms you need a substrate (carpet), a damp atmosphere (unventilated boot that has been opened in the UK) and spores (everywhere). I think the lower deep boot needs to be ventilated to stop mould growing in damp environments like the UK.
I suppose I should contact Tesla and ask for a replacement liner while it is still less than a year old. Could somebody please tell me the procedure for doing that in the UK. Thanks