It appears as if most all of the bolt locations should be accessible without much trouble as long as you can find where to drill.
On my 2005, I drilled up from the bottom, through the subfloor with a small drill bit in order to locate the holes. I then drilled down through the resulting holes in the subfloor with an oversized drill bit, being careful to not damage the mounting holes.
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Bob
2005 E350 Super Duty Ext Wheelchair Van
2002 Itasca 35U Motorhome