Hi,
I've had the same problem
I had done an ugly fiberglass shell to use a dive rite wings.
this wing had 2 problems, the first was that it was too hevy cause I had used polyester resin and not epoxy and too many fibergalss layers.
so there was a back trim difficult to prevent cause there was no space at the top of the shell to put a led bar.
I've dived this ugl shell for about 6 years before I decided I shoud change my system.
I've considered the hydrogom shell despite it's price (justified but expensive for me)
then I decided not to buy the hydrogom because the 9 kilos .
9 kilos behind is ok if the divers is in it's classicle position 45° let's say but not in the orther positions.
there is absolutly no perfect solution but the best trim configuration is reached when the lest is as close as possible from de gravity center and least from the line passing from the center of the divers head to the diver feet (feet joined of course).
in addition I think that in the hydrogom shell the horizontal tank is too far from the diver's bottom and I wanted to keep the horizontal tank.
for those reasons I built an epoxy/fiberglass shel, very ligth with enoug space to put a 3.6 kg lead bar on the top of the shell just behind the diver's scruff and 2 pocket of 2kg lest (small bags) in pockets situated on the divers shoulder's.
the result is better then what I excpected mutch betern there is absolutly no backward trim when I dive horizontaly I stay horitontal with not effort at all, when I am uprigth I stay upright without effort not to get backward.
in addition all my lest is dropable in case of loop drowning unlike the hydrogom solution where one can't drop the shell itself.
here is my shell... the only problem is that it is a very long job you can see it, it looks like a fiberglass kitchen sink as my wife says but it works well
epoxy fiber glass shell
regards