I bought my last carpet from Lowes. They sell several colors of carpet for boats. I bought dark charcoal for my trunk. I used the spray glue and apply it to the trunk area so I can slide my carpet around for a better fit. If you apply the glue to both and let it tack up, you can not slide it. Cut and trial fit before applying the glue. If you can cut the bottom and sides out of one piece it will look better, I think. You can start on one side and then spray the glue as you stick the carpet down. If you cut it short or have a bare spot you can cut a piece to fit and glue it in. In the trunk it's hard for someone to see your mistakes.
Have fun, it's easy and the material will cost about $20.
Dwight