Sometimes it is expedient to epoxy coat the entire part and then come back later and attach some sub parts. The rub is that you have to rough up the cured epoxy in the attachment area and sometimes that is not so easy to do.

So here is a trick I use;

Mark or layout the area that the sub part will attach and put some peel ply into the wet epoxy at that location. Use a bondo spreader to squeegee the peel ply onto the surface. Make sure it is flat and transluscent, with no air bubbles. Once the epoxy is cured and you're ready to attach the part, simply pull off the peel ply and glue your part on. 

The peel ply I use is actually aircraft fabric sold under the trade name of Polyfiber or Ceconite, is 3.2 oz, and is nicely bound on the edges to prevent fraying. I buy it onlne at Aircraft Spruce and Specialty by the 25 yd. roll in various widths, but you can buy it by the linear yard, 60 inches wide if you want to peel ply a large area. If you buy the material with a pinked edge, it is more likely to fray so don't use it where a finish will be applied as some fibers may remain embedded.