Don't sand them you will weaken them . They are not the strongest box to start with there are much stronger boxes available.

Not sure about them being poor quality. Always used futures boxes in sups with no issues. Stronger than fcs that I had heaps of issues with. they are raised from the foam to allow space for the cloth you use to cover the foam (glass or carbon). Then sand back for a flush finish.

Thanks for the input. I have enough carbon cloth for 2 all round patches...then I'll use the scraps to reinforce the forward ends...

Fitures boxes are bomber strong-they are not like standard Long boxes. 4-6oz carbon is fine if vacuumed if the HD foam block goes to the deck.

What martyman said.

They are awesome.
Sand after glassing. 2 layers of 6oz carbon running opposite bias...ie one at 0deg one at 45deg.

For best results you need to make sure the the cloth sits down in those sunken areas while the resin hardens.

I use narrow tape over the slots and slice the the carbon around the outside wall of the boxes with a razor blade. It helps to ensure there is no bridging. I fill any low points with q cell, then sand flush opening the boxes.

Then I cap the whole box area with 6oz biax and slice out the glass after curing or run a drill bit up and down the boxes as a dodgy router. Works great. I've flogged the living shat out of all of mine and the boxes have never budged.

You can put 20 layers over them and they wouldn't be get any stronger if you don't sand them flush and CAP over the entire box.

Get it? the T-nuts only have to break through the cheap plastic. All you are doing is putting 20 layers over the plastic flange. They must be sanded flush and whole box capped.

This is the Chinook box the original and by far the toughest box on the market . It's deeper with much larger area for the T-nuts to pull against . The Future's still work but have a very narrow area holding the T-nut . Put in a loose or narrow M6 T- Nut on the Futures far greater chance for it to rip out out compared to the Chinook . kiteboardingcloseouts.com/product/chinook-10-fin-box/

hilly said..
My Fanatic boxes failed and they were deep. Slingshot solid as a rock.

You do understand both are Asian generic boxes compared to Chinook, made in the US.

I call it luck, not higher quality in one or the other. I can post photos of broken Slingshot boxes if you don't believe. T-nuts broken right through the plastic.

they are made to be sanded flush -- I guess the concern is in removing some height, the plastic holding in the nuts is weakened? I've not seen any boxes fail due to this, but others above seem to have.

You could also router it in deeper, so the top of the box is level with board, glass right over it and then router the channel....with glass over top, that would make it really strong. Fill in the gap above the flange with epoxy/profil...heavier but strong.

Thanks. The base is set in place now with resin & fibres/'expanding foam resin'/glass cloth combo. Looks like about half the raised parts of the futures are sitting out. Will glass/carbon the crap out of it and see what happens...