Drainage is important, and you know that. I would use a water shield as an outer barrier. 2" poly isocyanulate inside that against 4" cinder/concrete block. I used 1/2" radiant tubing inside that and former the inside with mortar. These were mud bath tubs at a spa. 30yrs later they are still going. I am not sure what you would want to use for an internal finish. It would be nice to have a smooth finish. Seems it wouldn't matter in a mud tub, but would in a bathtub. Also, I guess it being outside you will need a cover as well as a cap for the walls.

You want modern at a good price, I'd go with a Wyndham collection tub. We're getting the 60" version of the Mermaid because space is tight. But it comes in 2 other sizes. We are replacing a 20+ yo whirlpool tub that hasn't been used in years due to the reasons you stated above. I just want something to relax in without the worry of gunky stuff shooting out the jets so we are opting for a soaking tub in our soon-to-be-remodeled MB. Here is a link that might be useful: Wyndham collection soaking tub

"I could also just get a pull-down faucet for the sink and aim it at the tub to fill it." You could - but you won't like it. The most one of those will fill is 2.2 gallons a minute - some less that that. Divide your tub's capacity by that and you're looking at 20 minutes to fill +/- Not good. beekeeper - I have one of these and have placed more than half a dozen in projects over the past few years. What you get for your money is a machined brass body that mounts in the ceiling or wall and a plated trim piece. The body is a substantial piece of hardware and chrome,brass, nickel plating costs $$$ too. Whether that's all worth 500 + bucks, is up to you. Like davidro says, it doesn't matter what the delivery system is, this is just an opening for hot water to come out of, albeit one with a bit of engineering. GD & Spanish - the splashing is very much dependent on the mounting height of the unit AND the tub selected AND the location of the water column inside the tub. Mine hardly splashes at all. The ones I have seen that splash only do so for a minute or so until their is enough of a pool in the tub to counteract it. Flat bottom tubs with tall ceilings are going to splash more than one from 7' into a sloped contact point in the tub. Besides , we're talking water in a bathroom, generally tiled so what's the big deal ??? It's not like the amount of splash is the same as taking a shower and leaving the door open. 2. While you are correct in that "the water cools off much more than it would from just a regular tub filler", it's not as if it cools off enough for anyone without a thermometer to tell a difference, and a very sensitive one at that! Sure the air cools the water more from a stream falling from 8 feet than one falling from two feet. But bath water that is 100 + degrees is not going to cool down to 90 deg. in the xtra 1-2 seconds it takes it to fall from the ceiling- get real. Additionally , that filler produces a very dense column of water (laminar) that has little to no air in it, so one might argue it will be hotter and less prone to heat loss than a "regular" filler that introduces room temp air into it's stream - thus cooling it off on it's way to the tub. So don't worry Spanish -your tub will still be plenty hot with that filler if you choose it. IT'S A NON -ISSUE people. I've already alluded to the real issue for lower tub temps - FILL TIME. That's directly related to the delivery system ( valve). If your valve and accompanying filler will only deliver 5 gallons a minute it's going to take a while to fill an 80 gallon tub, and there will be some heat loss. Select a valve that delivers 20 gallons a minute and you can be soaking quicker that most people can undress. Here is a link that might be useful: laminar valve body - see page 2

Thanks so much for the suggestions and advice. I am concerned about being able to get the tub close enough for a faucet reach but far away enough to clean. Unfortunately, a floor mount is not ideal since we're on a concrete slab. A wall mount would be a much easier install. It would be on a wall backing up to the master closet, so I think we could also have a panel to access the plumbing. I really like the Newport brass fixture, although it's a bit more modern than fixtures we've used in the other bathrooms. I would like to use a readily available brand name so parts are replaceable.