Will running plywood sideways sag?

[Hawg]

Everything I've ever learned about building says plywood is directional, it has to go across the floor supports in only one direction. The fish house frame I'm getting has 2 ft centers going across the 8 ft way. I'm using 3/4 treated plywood on the floor which is very stiff and the frame manufacturer claims everyone runs it sideways. (The frame only has a tougue 1/2 way back) I'm looking for opinions on which way to run it, my guess is most people in construction will say the right way and home builders, like me, will say they did it sideways. I think I'm going to tack in some center supports but I'm very curious if I'm just a nervous nelly and overthinking it.

[JSK76]

I can't really answer your question but I ran mine sideways with the tongue only halfway back and I ran into issues about 8 years down the road. I started to get some lift on the seams and some sags in the floor between the floor joist where the tongue wasn't running down the middle. Last year I went in and welded some angle iron brackets between the joist and now its fine. BTW I'm 2' on center so that's probably why.

[CANOPY SAM]

I'd wager you'd be better off running across the frame rails, rather than with the frame rails, but either way I'd add support brackets as was suggested above. I think the fact that the flooring spends so much of it's time so near water, or moisture, it's inherently prone to warp without additional support.