Ours flexed when we had our QB4. Didn't really notice it much unless you were watching someone else walk across the floor. Even though the longitudinal floor joists are on 16" centers, the transverse frame members that they sit on aren't. More like 4 feet spacing on those I think. So, 5/8" plywood on a 2x3, on top of a 4' spaced frame member, yes, it'll flex some. Not like a home by any means.
John and Rebecca Dickson
Emma-7 / Little John-5 / Iva-1
Full Timing Again, Rev B
2013 Ford F-350 Lariat CC LB PSD
2015 SOB TT - With OC's Awning Poles (#8)
At least in Heaven, RVs will be perfect, and I won't have to keep fixing them.