My experienced advice:
I have not worked on the one ninety, so i'm not an expert on the location of the drain plug. Dave is correct, there are posts on this site explaining right where to work.
After the inner hull drain hole and fixture screw holes are drilled, reach in and remove foam from a "pretty good area" around inside the hull. The idea being you want an unobstructed place for water to pool at the drain plug.
Then clean the surface area very well and use 3M94 primer and Sudbury elastomeric for the sealant. Though not really for structural use, the primer is a fantastic bonding agent, and no other adhesive really sticks to the material the hull is made of. With 3M94 primer, that thing will never leak.
Use some water proof plumbing grease, you can find it at your hardware store, or toilet bowl gasket wax for thread lube on the drain plug itself. That will keep it sealed up and easy to remove and install.
Martin