I need to make a secondary crawl space access door in the foundation of my house. It is a block foundation with a sill sitting on top. Do I need to be concerned with the locations and potential weakening of the building structure and outside walls? Would I be okay with just a 2 x 4 header turned upright nailed together supporting the sill, transferring the weight to two 2x8s joined together on each side? Thinking about tackling this project myself? Any recommendations?