cabin air filter

I am looking to install a cabin air filter on my 98 jetta, any thoughts as to what is the best route to explore? I found some posts on putting an A4 assembly on the A3, but not sure what is exactly needed. I found an assembly off a 2000 jetta on ebay but it is just the box nothing esle. Would i need just the box and a filter? thanks for any replies

Just buy a kit ready to install. parts4vw.com has one, works well. I put one on my old jetta.