Do you put the blueboard over the edge of fibreglass base or set it on top.there is a lip on the base.

Why are you using blue/green board on shower walls. Not recommended, should be using cement backer and then thin set (powder) as the adhesive. UNLESS you're installing a membrane such as Kerdi, in which case regular wall board is recommended.

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Jaz

I agree. Only cement board should be used on the shower walls and it should come to about 1/8 to 1/4" above the top of the base over the lip which you will caulk with 100% silicone caulk as well as the corners of the surround after taping with the correct tape for cement board and thinset. Do Not grout the corners or bottom edge of the tiles.

I would rest the cement board on top of the shower pan lip.
Fill void with thin set and let the tile hang down with a 1/8” gap at the bottom between tile and pan.
Grout and caulk to finish
Get r done:)

You can do it ether way if you go over the top of the tub it will push the rock out a 1/8 inch you will notice it if you have wall paper on the wall if you cut it back you can fill it with durabond setting compound and tape it with paper tape I think cutting it back looks the best which ever way you do it be sure after you paint caulk around the tub