Thanks for all the suggestions, I think I am going to folllow all the advice, I can't bear to be without her!
takethefifth: Symptoms were a small puddle of water in the rear nearside passenger footwell, but she sits on an incline, so I couldnt nail it down to leaky membranes, bulkhead/scuttle etc. And yes, I also get steamed windows. Often takes me 10 minutes to clear up the water from these with a sponge and leather. She has also started to get mould on the seats/seat belts/felt roof lining.
darnpistonbroke: ECU - she doesn't have many electrics (thankfully!), but your suggestion for the scuttle drains is good.
I am sourcing the waterproof duck-tape from a local boat repairers as the stuff I have seen so far was pants!
rowlers: Having read gibby's link, I have decided to replace all the grommets as a precaution too, thanks!
So now I have my parts on order, just got to wait for some fine weather and a couple of days holiday to get the work done.
Thanks for all your help everyone