Good morning, Jamus~
Here are the dimensions I developed for a sit-up blind on my Sneakbox. We sat on spackle buckets and the "sill" was 34 inches above the floorboards.. With milk crates, you could go a couple inches lower. These heights, of course, presume you have some sort of flaps. We lowered the front one to shoot. It can be a bit lower than mine - but the rear should be higher than your heads.
In addition to a better hide, the folding flaps are nice because the grass/vegetation is protected when down.
Hope this helps!
SJS
Steven Jay Sanford
Pencil Brook Farm
South Cambridge, NY
http://www.stevenjaysanford.com
Here are the dimensions I developed for a sit-up blind on my Sneakbox. We sat on spackle buckets and the "sill" was 34 inches above the floorboards.. With milk crates, you could go a couple inches lower. These heights, of course, presume you have some sort of flaps. We lowered the front one to shoot. It can be a bit lower than mine - but the rear should be higher than your heads.
In addition to a better hide, the folding flaps are nice because the grass/vegetation is protected when down.

Hope this helps!
SJS
Steven Jay Sanford
Pencil Brook Farm
South Cambridge, NY
http://www.stevenjaysanford.com