Floating boathouse foundations. when a permanent support structure is not feasible for your boathouse (due to fluctuating water levels), we custom design floating boathouse foundations & support structures for boathouses.. Floating boathouse plans. floating boathouse plans: included in the free workbench plan is a blueprint, step-by-step building instructions, a list of tools and materials needed, as well as user comments.are you new to woodworking and looking for free woodworking projects, plans, tips, ideas & more? look no further!. Building a floating boathouse is not an impossible diy project; however, it does take some planning and commitment. the most important part of your new boathouse will be the floating foundation. this simple how-to guide will walk you through the basics of creating a foundation for a boathouse. step 1 - plan your home.