Shower conversion

[Kim_in_FL]

Hello! First time DIY chick here, but fear not! I’m the handyman of the house and love to learn how things work. I have a GC friend and a neighbor expert DIY’er. I am converting my daughter's bathtub to a shower. I have torn out everything down to the studs, taken the tub out, removed the plumbing fixtures, and have dug down to locate the P-trap and removed all the 1 1/2” pvc. It’s on a slab and I’m using a Woodbridge prefab base with left drain. Spent multiple trips to Lowe’s and Home Depot trying to get the configuration to work. 45’s were too short horizontally, 90’s were too long. 60’s are just right. It’s a tight fit. A few questions before I wet fit and make it permanent:
1) 1st photo is the existing. Should I assumed it’s vented if there’s water in the p trap, and no prior issues with drainage?
2) 2nd photo I’ve placed the vertical pipe to show where drain will be. From center to center is 5" horizontally. From the top of the existing to top of slab is 7 1/2" vertically.
3) 3rd photo is dry fit configuration. Does it look ok? I'm going to replace the top riser section with a longer piece to work with then cut it back. I'll back fill the hole with sand up to the slab portion. Can I use self-leveling mortar to get it flush with existing slab, or does it have to be concrete mix?
4) Instructions for base are very vague (attached). I don't need to use a pan liner, but should I, to make it easier if base ever needs to be removed? So pan liner on slab, then thin set to set shower base...or should I just get some roofing paper? (for walls I'm using the waterproof hardy backer boards with the red stuff for waterproofing)

Thanks in advance!

 

[Reach4]

How are you going to line up the trap with the base?

shows what looks like a good way to me.

 

[Sponsor]

 

[Kim_in_FL]

How are you going to line up the trap with the base?

shows what looks like a good way to me.

I’ve already got it lined up perfectly as it is dry fitted

 

[CENTRALFL]

Replying not as a pro, just another DIYer that has watched a few videos so take it with a grain of salt.

The instructions mention thinsetting the pan to the substrate (in this case concrete slab). So it would seem your plan of decoupling the pan from the slab via a pan liner or felt paper would not be a good idea. That is aside from the fact that if you happen to get a leak somewhere, the water had no where to go and would be trapped by the pan liner as it has no slope and is not tied to the drain.

From what I've seen, opportunities for flexing should be minimized as these pan will crack if they flex. And cracks lead to leaks. I've even seen mentions of doing SLC (self leveling compound) on slab to get it perfectly straight and level, though that depends on how level your concrete is. Prefab pans have built in slope towards the drain, and any deviation from level would negate some of that slope.

Make sure to look at min max thickness of any concrete products. For example, SLC, some will go down to feather up to about 2-3 inches but they require a structural substrate (like existing concrete slab). I don't think it can be used to fill in a hole in slab by itself. Also keep in mind cure times of various concrete products.