when i removed my old one it was spot welded every 10 inches and was rusted all around them so theoretically the new boot panel is a hell of a lot more secure,
1. Self tapping bolts(with nylon lockers on the tother side, just couldnt be bothered to drill the hole) all around the horizontal surfaces.
2.rivets all around the vertical sides
3.evo - stick serious stuff ultra between all ajoining surfaces.
4.a couple of coats of hammerite on the interior side
5.a couple of coats of hammerite undercarriage on the underneath of the panel to make sure it lasts another 15 years.
EDIT: I must also add that it passed its MOT with the abomination of the old boot floor and it had no carpet or soundproofing when it went in. so it was in plain sight, So surely having a boot that is securely fixed in (but not welded) is much better than not having a boot at all (like it was).