Dear Bryan;
That's a neat idea & might work well for hand sanding a large flat area as one could use both hands etc.
Way 'out of line' on price though.
The BEST "long board" (2 X 17") sander is sold by Craftsman for around $130.00 and is air operated. It works great if NOT over presurized (has 90 psi limit) while in use.
That's a 2X17 version of the 3X9 sanding block (one hand) is all, with holes added for the welding rods. A 3X9 flexible sanding block sells for under $15.00 (new) here in California and it would be worth a try for $18-$25.
Next time I'm at my supplier, I'll see what they know this new item.
Good luck.
