like i said before in other threads,
get like 5 rolls of painters tape*like the blue one* tape off your trunk every little bit,and top of your box too if you want and sides, and then get expanding foam spray it between the gaps let it settle get hard, then get a scalper/box cutter,and cut everything nice and square clean it up,and PROBLEM SOLVED..
and then
in the future when ever you decide to rip it out, work backwards, take the box out peel the tape off, and PRESTO, brand new trunk again.