ron1 replied:

i got a trailer sailer and used high density foam when i decked it out, about 2" cant quite remember and the boats on the hard stands so cant have a look ,but feels fine and feels thick enough, mind you there on a flat area,

Chris (W.A.) replied:

Go the four - six inch mattress from Clark rubber - $100 - $200 but it's worth it when it comes to the missus.Nice southerly coastal fishing trip someday.
Chris

phil replied:

Don't go for anything less than 100mm. I started out with 50mm medium density foam, as used in swag mattresses, but found that I "bottomed out". My foam supplier laminated another piece of 50mm high density foam to the original. It still just fitted back in the original cover and he only charged me for the foam. I use it with the softer foam on top and it is really comfortable. It can still be rolled up for storage at home but I leave it flat in the back of my ute camper setup with a cheap blue tarp and a piece of old carpet on top for protection so I can load other items on top.
Phil