I've used a Dunlop automotive trim adhesive when I've replaced these in the past. I've no idea what is aqvailable your side of the pond.

Normally I leave the part nearest the screen loose, the finisher round the screen holds it down, and put some glue at both ends and above the speedo. Onviously remove the finisher on the dash and use it to hold the pad down on the surface of the dash. Last time I used a small gas powered soldering iron to make the holes to put the finisher back on the dash.

I think that if you stick the dash top down really well, then on a hot day the metal dash expands at a different rate to the foam dash top, and hence over a period of time the top starts to crack. Of course this theory may be a load of rubbish.

Regards