I'm glad I listened to Havasu's suggestion about using hot glue. Man, the newer stuff is so much better than the old stuff I remembered. I got a Gorilla mini dual temp hot glue gun. It's nice and compact so I have room to set it down when not in use and it fits my hand very well. No strain when pulling the trigger. I've gone through a LOT of those Gorilla glue sticks. It is so much easier than I remembered and this glue really holds. Grabs almost instantly & then stays put. It doesn't stick to the sink or countertop though so dribbles and strings are easy cleanup.
I bought more paint stir sticks and jumbo craft sticks because I ran out of both. I realized that the right wall has a bow in the middle so it sticks out more there than on the edges and I need to compensate for that.
I really want to try a dry fit of a side cementboard piece but I'm not sure if I can lift the board into place & I don't want to make my stupid arm worse.
I took some pics but the angles are crap. I had a hard time finding a decent position to try to get the right view.
Left side: I'm making a note to not screw through the craft sticks that are sitting on top- they are there to have support for the board. I got it a bit skewed toward the back wall but I'm hoping that won't be a problem. Worst case scenario, I can add in more shims in that area, but I'm hoping that won't be an issue.
Right side- I put sticks around where the hole will be drilled for the controls. I think it's 2-5/8". Need to figure out how to get the pilot bit to attach to the holesaw arbor thingy. I should probably add sticks near the tub spout hole.
Wonky center pic
Need a little advice though: Since the tub slopes down to the right and I had to use 5 shims (but different ends with different thicknesses) on the right side vs 2 shims (which on the left gets me a 1/4" gap), should I shim up the right side cementboard the same amount as the right end of the back cement board? Or should I go with 1/4" gap? Or somewhere in between. I believe the mustee thing can sit flush to the tub edge but obviously it will have to be shimmed on the right side so it will be level. I need to have less than 1/2" gap from the surround and the tub. I'm using 3/4" instatrim to cover the gaps (although it isn't quite 3/4" coverage. The 3/4" is the hypotenuse measurement I think). In the event that the cementboard ends up being lower than the surround on the right side, I'm hoping it will be hidden with the instatrim.
In terms of it being flush/straight etc I'm going to try to remedy any minor imperfections with thinset.