Hi again.
After much cogitation and after buying some J – B Weld Plastic Bonder ( as recommended in one of the links you sent me), I ended up using masking tape to hold the deck in place and thin cyano run into the joint. I then ran a bead of thick cyano into the joint from underneath. It's in and it looks fine. When I tested the J – B Weld, I found it to be no better than epoxy with ABS; it peeled off quite easily. And, yes, I did roughen the surface of the test piece and I degreased it thoroughly.
As I said before, while I would have preferred to use the UHU Plus Acrylit Express, the curing time seemed to me too short to do everything that needed to be done to fit the deck after spreading the adhesive along the joint on the hull. As I also said earlier, I've been caught that way before.
One thing I did was cut the deck into two halves so I could deal with each end separately (I came across this suggestion in another forum). When I'd adjusted the two halves of the deck to fit their respective ends of the hull, I found that there was about 5mm overlap at the cut ends of the deck. Cutting this overlap off at the join was a lot easier than trimming the excess at the front and/or rear of the deck while keeping the correct shape would have been. If you see what i mean.
Anyway, thanks for your help and I'll keep your helpful suggestions in mind.
Thanks again,
John