We have cruising friends that did this. It added 80-90lbs of weight and within a year the foam had started to "melt" and deform badly. Really misshapen and almost not usable because the foam breaks and starts to hinge all over.
So if you want to spend a bit of money
, add a lot of weight, and get a few months more life out of it - go for it!
BTW, if you do go for it (I recommend against), make sure you have experience with 2-part foam. This isn't a "mix it up and pour it in" thing - if you don't have experience with it, you will have a disaster and a mess of epic proportion.