You could just use a pure sealant like silicone (most of them are neutral cure now and don't damage metals), but really for this job an adhesive sealant is better, as it will stretch instead of detaching and opening a small gap like any pure sealant would on a highly stressed part that can move a little when the hull flexes under load.
Sikaflex 291i is using PU chemistry and no longer (finally even officially) recommended for exterior use. You want a modern MS polymer sealant like Sikaflex 591 or any other product with this chemistry.
Come removal time the usual solution is to bash a putty knife between the parts to cut the adhesive.