There is an advantage to Protec, your whole tub is insulated, not just 3 walls.
Second, you can order your tub with the pack plumbing in one of 9 places this will help you in building into the deck, for a cleaner look and easier access. You sevice techs understand what I mean when you have to get to an equipment area and their is a 2" x 6" header in the way.
Third because the equipment isn't under the step, the steps into the tub are reinforced, so a in deck situation you can step in as if it is a commercial spa application. Most companies don't want you stepping in on their cool down bench because they do not support it, so they say it is safer to sit on the top rail and roate down to the cool down seat.
The way we ship the tubs doesn't make it any more expensive to ship. I have seen higher shipping rates by other companies. Yes we do offer it both ways, but we sell over 90% protec.
I have seen several dozen deck applications including 1 that has the pack about 10' from the tub that is inside their 3 seasons porch.
But Chas is right. They make a very comfortable tub. I have been in this industry 20 years as a service tech, sales man, a manager a store owner and now a rep. I have sat in dozens of brands and hundreds of models and I will tell you if you are not comfortable in the tub you will not use it as much.