backboxes

Hi all, Just like to say hello first of all as this is my first post. My name is Paul and I drive a 2003 VW Polo 9N She's my baby and i've really been working hard on her to get her up to the standard I want! So here's a spec list! 2003 Polo SE (mk6) Tinted glass PAS E/W R/C/L...

Thinking of getting a backbox for my ibiza, and am unsure which to get. Was thinking of either a twin 3", or a 6"x4" oval. Also, would i have to trim the bumper to fit it on, and how would i go about it? its going on a 2003 1.4 16v.