Larry C wrote:I highly recommend using a long board throughout your build.
That is a proper boatbuilder's longboard - though I have seen an eight-foot two-person board being used on flat work - and my former boatbuilder boss putting six guys on a length of two-inch plastic pipe wrapped with sandpaper to get his own boat's bottom to have a perfectly fair bottom....
I would suggest, for all sorts of purposes, having 'shortboards' too. As you say, power sanders just leave any bumps untouched except to put a smooth finish on their surface. 3M sell a very nice longboard for auto refinishing as shown below but the self-adhesive strips for it are the really useful item. I use them to stick onto perfectly square-edged pieces of MDF to make wood files - they cover a large enough area to make any surface flat and because they are rock hard, they cut only on the high spots and don't touch the low spots. So a few minutes rubbing with either of these will remove anything that isn't flat - for example, getting the filler over a screw/nail head perfectly flat with the surrounding surface.