wet trunck area

hello!
im new to this forum,but have been following your old topics for awile now,im from italy and jimnys' are not so known here as in other countries,here they are stuck on jeeps and range rovers,be growing up in the states ive had a number of older jeeps and samurais...anyway the sami's performed much better in my opinion,but always lacked power:(

anyway my problem is that every time i go wheeling i have a wet trunck and a bad smell of the dirty water,has anybody the same problem? i have heard that jimnys have bad trunck lining and holds water,is this true? and if anybody can tell me how to seal it!