OK....so....
There are two clips per side, one each in the forward and aft inboard corners that retain the seals.
There are the two tabs each side that retain the tops when fitted.....the tabs poke out at the top when the bracket is mounted correctly.
I'd personally use 3M weatherstrip adhesive to retain the seals. A person I know has had the same problem as yourself regarding weather strip thickness......he cut timber battens to sit against the seal (and under the bottom of the seal channel) then used G clamps to clamp the seal and apply pressure.....left it that way for a week or two....when the timber was removed, the roof panels fitted perfectly and the seals were sitting perfect in the channels. Just an idea for you.