Sorry for the long deal, been swamped with work. I have a converted cargo trailer so my walls are straight and covered with 3/8 plywood, making attaching styrofoam very, very easy. I just used 1 1/2 inch screws with washers on them to go through the styrofoam and into the plywood. My styrofoam has an aluminum foil covering on one side, so I turned that into the inside and left it bare. I don't care about looks, but it would have been very easy to put paneling up over the styro. Since you already have 1x4 runners on your walls, it would be very easy for you to do the same. The styro should easily bend to the curves of the walls. On the roof I put 3 layers of 3/4 inch styro. The 3/4 is very flexible and easily bends to the curve of the roof. It is held up with sheet metal screws and washers screwed into the ribs. <br><br>If you are getting your fiberglass from worksites, does that mean it is 3 1/2 inch? If you put it on both walls, won't you loose 7 inches of living space? To me that is way to much!! Have fun! Bob<br>