z3 insert instructions? help...

i have a 97 civic and i want z3 fenders....i can get the whole fenders for 160 or the inserts for just 35....i'm thinking of getting the inserts...but they're plastic, so that means i can't just weld them in. I have basic knowledge of autobody, but how would i attatch them after i cut the hole? and would it be VERY difficult to make them blend in...like perfectly......(well duh it'll be hard...but possible?? for me??)

any tips for attatching them? bending a little metal inward maybe? something to adhere it too?..not sure...i just need some tips...or maybe i should go with the whole fenders.