Eric,

If you sanded the panels with 150-220 before staining and they look good there's no reason to sand them again. You're right, it'll take the stain right off. I've done stain two ways, one was just stain, assemble, touch up any blemishes caused by assembly then fiberglassed. The other was stain, roll on thin coat of epoxy, assemble, stain anything sanded off during assembly, fiberglass. Both ways worked, I found as long as I'm careful during assembly the first method was my prefered.

George K

   Thanks for your advice, George.  I did do a thorough sanding of the panels prior to staining and they still look pretty smooth in most places, so I will just touch up the few rough spots and roundovers and proceed to the glassing.  

fwiw, depending on the stain and patterns, i have had good success with a quck skim coat of epoxy prior to glassing....which was important at least for me, to ensure i kept the epoxy from lifting the stain and moving it onto an adjacent unstained surface.

in my case, i masked off the unstained part, skim coated over the stained part. let it set then did glassing.

this is not an issue if you are not dealing with sharp lines.  but whenever you epoxy over these alcohol-based stains, you will see the stain lifting into the epoxy and if you start to work that epoxy aggresively with spreader or brush, it will start to move around. 

the important thing on a skim coat is to roll it on and move on.....and not try to 'rework' any area.  you are just trying to lock it into place with the least physical action that would promote the  lifting and moving of the stain.

h    

Thanks, hspira.  Fortunately, I am staining the board all in one color, but will keep that skim coating/masking tip in mind when I apply a maple veneer pattern to the deck.