It really isn't as hard as it sounds. The first thing is to know where the ribs are so you don't cut one. Most vents are 14x14 in the USA and they often come with a cutting template. Mark the hole to be cut, drill holes in the roof and use a jig saw to cut it out. The design of the headliner varies so much by van that I can't really give you details. Some vans will have a layer of plywood under the roof, but most won't. You will have to cut the headliner to fit the vent. Dry fit the trim piece and the vent so you understand how they go together and how they can be screwed together before going any further. <br /><br />Putty tape is your best choice. On some vans the roof isn't smooth, it may be ribbed sortof. Then you will have to use the tape to build up the valley in the ribs to make it smooth. Be sure to put in enough so it is under pressure when you screw down the vent and is completely filled in. <br /><br />Then use the screws that came with it to attach the vent. The pressure form the screws should squeeze out some putty tape, cut that off with a knife. Put a bead of caulk all around the outside of the vent as a double-protection and a dab over all the screws. Dicor is one of the very best and available at RV stores.<br /><br />Go down below and attach the trim piece and you are done. Bob
