Draw a level line on the wall where the bottom of the lip will go.
Fix a wooden batten down the side and across the end.
Cut the pipes ready to plumb in, I do up the nuts withthe bath out and use the push fits as the last connection, measure up the location of the waste and assemble the pipework.
I wanted this bath lower than usual hence the hole in the screede.
Then silicone the top of the batten and the wall and set the bath on the batten, silicone the top edge.
My memory is vague but I think that I threw the legs away and built a nice wood frame to support the side and end and oak panelled it in. No problems yet (2017)