Hi Tony,
Hi John, Alan and Angela Here. Your right i take the old vinyl off with a heat gun then loads of pva until it is sealed then vinyl coat paint Just done one with speaker holes layered the back with fibreglass where holes were then p38 filler gentle sanding loads of pva then paint as before, I always cut mine about 1"1/2 shorter for ease of refitting. If there is a gap on the ends from inside the boot its possible to push some sponge under the sde trim to bring it out, better then bending the cardboard trim and damageing all your work
Alan.