Joining together the top and bottom of a sub has never been easy, but with a little patience it can be done,here is an idea.
First thing to do is get the mouldings in line, dont worry about the gaps at this stage, you can get them in line by use of part bulheads and careful use of a hot air gun or even boiling water in smaller places. Once you are satisfied with the alignment then next tackle the gaps. Careful use of sandpaper and file to get deckline right, once thats done all should be well apart from those gaps.
Grease over the joint on the lower half of the hull and then tape the top and bottom into position with a few well placed lenghs of tape at the points where the two halves touch.
Carfully spread filler over the joint , do not worry if it spreads over onto the lower half as it wont stick due to the grease, once it has set then carfully sand down until you reach the fibre glass being careful not to sand off any details. Oce the lower hull is clear of filler and there is non left to keep the two halves joined you can take off the tape and release the two halves.
The top half will now have a bead of filler attached but it will look a bit shabby so clean it up carefully so it looks presentable. Now it will not stick too well to that fine edge on the glass so it will need reinforcing on the inside with either grp resin/matt ot I use Devcon Plastic Welder, this is aa epoxy glue that hold plastic permantly---Job done!