I would do one with the flange on three sides that is specifically made for alcove installation. A drop in, since the lip is higher than the surround, creates a channel for water to lay in next to the wall --they aren't the best if you want a shower, too. An undermount can work but the waterproofing needs to be done carefully around the deck. The simplest solution is to use a tub made for alcove installation. There are a lot to choose from .