Installing a bathtub.

So, I've been reading for a while about installing a tub. I did all the plumbing and the drains. Everything is ready to install. I have to build the wall behind the tub though. Two sides are ready to go with the plumbing installed. The floor is slightly off, so I am going to set the tub in an inch of mortar and level it out. I would like to set the tub in mortar,hook up the drain, and then build the back wall afterwards. I have full access behind it and the shower walls are direct to stud. Is there any reason why this wouldn't be the right thing to do?