dont try and do it without primer
if you do, give it a month and your spolier will look like what it did the day it turned up at your doorstep..........paintless
rub the spoiler down with some 600, dont go to mad tho, make sure all the shit is off it (normaly has flakey shit on it)
Primer
dry
Rub with wet and dry (1000) till its really smooth and peel free
Paint
dry
Laquer
dry
Rub with more 1000g till it looks dull (depending on how much laquer you use, dont rub to much) just till its a dull colour
then buff with corse compound
then fine (both with buffer)
then polish
will come out like glass and will last forever
as for fitting......not sure mate