I have used RTV / Silicon Sealant for years with great results. You actually "glue" the cowl to the fuselage. The trick is where to apply and how much. If you have wood blocks that stand off the firewall you apply a liberal amount to the blocks insuring it gets into the predrilled holes. When you secure it with screws/washers the RTV acts as a mild thread lock and will also form a silicon sleeve as depicted in post #2. Removing the cowl is accomplished by inserting a thin blade E-Prop or similar between the fuse and cowl to break the RTV bond. If you have a setup where the cowl slides over a Fiberglass fuselage "lip" you apply the RTV to the flat sides of the cowl only. - Stay away from the corners of the cowl with the RTV as they will not allow the insertion of the removal tool. Apply the RTV in 1" widths only where your pre drilled bolt holes are located. I have several Giant scale warbirds which contain a pound or more of leadshot/epoxy mix glued to the front inside of the cowl for balance and this method has worked perfect.