The framing strips are expanded PVC and bonded to the interior roof with a thick bead of Window weld. They are more flexible than wood and plenty strong to support the AC and keep it from jiggling. We double them up when installing roof top air conditioners. They are essential if the span between the OEM roof beams is more than 18".
AC Adapter Install procedure: We recommend 3m Window-weld or Sikaflex 221 adhesive. Locate and cut the hole. You can use the adapter as a guide to mark the hole. Stay clear of roof supports, obviously. Make a tape line 1/4" beyond the adapter perimeter. De-gloss the area with a Scotch- brite pad. No need to scuff. Just dull the paint. Clean with isopropyl alcohol and let dry thoroughly. Blow dryer if it's wet and/or cold out. Apply a good amount of the Window-weld on the face of the adapter. Then press the adapter down onto the roof until the adhesive oozes out the sides. It's not necessary to clamp. If you do, use a lot of lightly set clamps and spread out the clamp force over the whole surface area. Using the adhesive that oozes out, make a fillet around the adapter with a double gloved finger. Pull the tape within 15 minutes. Cure is fast on outside. Let cure overnight and then proceed with the AC install per the AC instruction. Seal the adapter and onto the roof about 1/2" with Dicor self leveling sealant or Flexseal from the TV guy works well. Good idea to check the integrity and reapply the sealant every so often.
Van owner and/or installer assumes all risk associated with roof top mounted items and/or components. Van owner and/or installer recognizes and agrees that this product, and each of its component parts, is sold “as is” and that seller makes no representation or warranty of merchantability that the product is fit for any particular purpose.