plasterboard tape and tank around bath?

[paul flight]

sorry mate but the seals will not work . this bath must be supported . spend some time getting this right qoz now you have started it the ball is in your court . you may have to go back later and spend more time and money .

 

[DHTiling]

As faithy has said, if you use a support frame around the wall and sit the bath on this.. then no matter what movement is in the floor boards the bath will not flex.

My bro who does bathrooms etc day in day out always frames the bath for a more solid installation.