I am replacing the T1-11 plywood siding on my Bay house. I am painting (roller & brush) 4x8 sheets on the ground before I install them. On the front of the siding I am using Behr Premium Plus Exterior Primer followed by Behr Premium Plus Exterior Flat. My situation is that I want to seal the back side of the 4x8 sheets but I want to try to save some money too. The new wood really soaks up the primer ($90/5gal.), but I can buy mixed matched Behr Premium Exterior semi-gloss at clearance prices ($25/5gal.) So my question is. Can I use the semi-gloss to seal the backside of the panels since they will not be exposed, and the color does not matter? Or should I use the regular primer? Any suggestions?