Thanks for the comments. The liquid is runny - like cold black coffee. It leaks out when moving the camper after being stationary for a while so I'm thinking I have a rain leak somewhere, it's building up and getting stained dark inside the structure somewhere. Doesn't sound good Inside is dry so not sure of the exact construction. It has all dripped out in a few minutes but does come back after time.
Regarding the battery - as I suspected - the 130AH battery is an after thought. Good idea for non-mains power but need to make the setup a bit tidier and neater. Was obviously installed at speed!
couple of things then,
buy your self off ebay, a meter damp meter £ 6.90
and go all over the interior and see where its damp, It sounds (as you say) like ingress then finding its own way out again,
common but fixable problem with Apollo
And in terms of weight distribution personally I would move that battery as far forward as you can, mine has its battery box on the floor against headboard for example
As I mentioned Kris, mine has some sealant applied at manufacture 'oozing' from various points where metal edging has been applied, and especially in the underside corner rails where it sits on truck bed
I imagine it get squeezed out of there on bumps on road surface I don't try and clean it up as that stuff just smears everywhere and its best left alone instead