: I have been wondering about the board too. Can you use a piece of
: masonite?
Yes, or doorskin (1/8 ply)
This is for flexible board that I'd use on a kayak.

:And couldn't I use some spray adhesive?
Yes. If you epoxy-coat the board it makes it easier to get the paper and glue off when it's time for new paper.

: Or make a board with handles
I usually glue a couple of v. small blocks near the ends of the board- you don't want to create a flat in your board, though.

:that you can wrap the paper around and
: clamp it at both ends.
Once you stretch/clamp the paper you pretty much lose the ability to bend the board to a curve.

If you have the $, just get yourself the 3M product (and a bunch of paper, I suppose)
http://solutions.3m.com/wps/portal/3M/en_US/Marine/Home/Products/Catalog/?PC_7_RJH9U5230GE3E02LECIE20S4K7000000_nid=3X4M3MFZSJbe4CCRDFQ26Jgl

: BTW I see sandpaper for sale at flea markets and other used places
: (the paper isn't used LOL). It helps to know what things cost
: ahead of time. Lot's of times I see things that they want more
: for it there then If I got it retail.

And some of that sandpaper is junk, to boot.
I like Mirka (or Norton) paper. In spite of my 3M mention above, I'm not a fan of 3M paper.