I do not know if yours are 2 x 4 or 2 x 3 layed flat.
This might help. This is a 97 T2653 floor overhaul by EMD_Driver. He did a great job.
To the OSB, Sunline may have had OSB made for them or got it on the industrial market. Many times the floor was all one sheet, no joints.
I have 1/2" (yes a full 1/2" as 2 of then create a full 1") in my slide floor. Point is, Sunline was able to get real 1/2" not the reduced size we see in the lumber yards.
That said, I do not know what your floor is, 1/2", 5/8 or 3/4" just stating that the nominal size can be actual.
I myself would replace the flooring with exterior glue plywood. It's a personal choice, both will work.
Hope this helps
Current Sunlines: 2004 T310SR, 2004 T1950, 2004 T2475, 2007 T2499, 2004 T317SR
Prior Sunlines: 2004 T2499 - Fern Blue
2005 Ford F350 Lariat, 6.8L V10 W/ 4.10 rear axle, CC, Short Bed, SRW. Reese HP trunnion bar hitch W/ HP DC
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