I got tired of building heavy wood or plastic battery trays inside the fuselage so instead I printed this strap guide which is in-layed on the bottom, outside of the fuselage. The fuse floor should be at least 10mm thick in this area as the guide is 4mm deep. This guide will distribute the load from the strap accross a wide area and it also makes it very easy to change strap sizes. The depth of the guide will accomodate most strap buckles if you choose to put them outside and it also keeps the strap from being damaged on landing. Inside the fuse I glue down strips of velcro to help stabilize the pack.