It is a very good idea. Maybe better if you cut the PVC into small
pieces so individual ones can roll as you pull sheets out and the sheet
doesn't have to just slide over them.
My cart, which will be rebuilt soon was about 13" wide. This is WAY
too skinny. I will likley go 18" inside and figure out riggers to get
to 2' or so. I also plan to drop the sheet goods down to lower the
center of gravity. A 1" piece of HDF is VERY heavy, not stable, and a
danger in a cart if not built correctly.
I would also recommend dividers in the cart to keep sheets from
shifting against each other. When they do it makes it very difficult
to remove them.
Locking casters are a must, otherwise the cart is sliding around when
you are trying to put in/take out sheets.