So my 2007 in was I'd like to say good condition with little to no rear rust under it needed to perform an emegency boat launch yesterday - its never been dunked before and its a river so not salt.

Get it off as the slip is rubbish the water came up to about 20cms below the bottom of the tailgate, which should be ok according to what I read.

Bot off drove off and notice loads of water pouring out the wheel well and every other orifice... then I noticed I had no sound on the radio and the speaks were making a quiet crackling sound.

I checked the amp no water in the no but it was soaking wet. I disconnected it and am going to leave it to dry n the meantime I will be praying...

Is this meant to be like this or has something gone wrong? Current stable:
2006 BMW M6
2007 4.2 V8 S/C FF
Gone:
2002 4.4 V8 FF

There should be bungs in the holes in the spare wheel well. May be that you have some missing which is allowing ingress of water. Needs checking. John
2008 Stornoway Grey 3.6 Tdv8 Vogue
2005 TD6 Java Black Vogue - Written off!!
GAP iiD BT
2003 Discovery TD5 Auto, Nanocom Evolution - gone to a new home!
MasseyFerguson 152 - No electronics!! - Sold

Usually people take the bungs out of the bottom of the spare wheel recess in order to let the rainwater out that has leaked into the car.
It appears your car successfully achieves this.

I needed some humour to the situation - tbh guess there's no harm leaving them out so long as I know where they are to put back in if I'm ever wading again Current stable:
2006 BMW M6
2007 4.2 V8 S/C FF
Gone:
2002 4.4 V8 FF