In 1990, during the restoration of my early TR3A, I saved the original seal for the trunk lid and put in new seals as they had been originally.
There is a long piece which goes down one side - then turns the corner, the goeas up the other side. The seal flares towards the outside and there are no cuts or mitres in the lower corners.
There is a second piece cut to fit all across the top. This is angled inwards towards the trunk opening so as to not interfere with the hinges of the securing studs.
Originally, both seal pieces had been glued down into the channel that supports the seal pieces. But in 1990, I cut the pieces a bit longer than needed in case some schrinkage occurred later. I have run it like this for the next 112,000 miles with these seals not glued in. It has neven leaked and when I want to clean out the boot and this channel area, I just pull out the seal pieces, clean it and then put the seals back into place.
Don Elliott, Original Owner, 1958 TR3A