here is a pic of mine before the refit

i used ratchet straps from corner to corner
when i bought the van in 2006 i asked for the braking strain of the anchour points in the van and was told that they could each take a ton ,so with that in mind and some big straps off i went
four years later the thing still had not moved it had 600 ltrs in most days
you will need to baffle it though with lenghts of land drainage pipe
works a treat
Andy