We just renovated and actually created an indoor spa "hot tub room". We needed to do a few things to make it viable for the indoors (as it does keep the water in all the time and stays hot).

It comes with a thick cover so that's important when not in use.

We have a cement floor underneath and we tiled the entire floor.

We also installed an exhaust fan (one of the 3 in ones that also have light and heat).

We installed a drain, but did not worry about a tap as we can fill the hot tub from the hose (once filled it stays in unless we drain it).

Hope that helps. An enclosed porch should be similar, but probably less of a worry than in a master bedroom as we have :)