3M outdoor mounting tape also sold as automotive trim mounting tape. Its gray foam double stick.
Prep the surfaces well.
Any glue based attachment (double stick tape is essentially a glue) will eventually fail... but this stuff is very good.
Another idea is mount them on rods that can be raised or lowered, attached to the side/back rails. Pull them up when at speed kind of like dealing with a stern mount trolling motor on a jon boat.