A simple way of thinking about full foam,
Where is the equipment compartment and what is between it and the elements?
If the only thing between the pump and heater is just a wood door or has vents to let heat out
you actually have plumbing on an outside wall, when you think about it, you wouldn't insulate a house that way, so why would you want a hot tub sitting out in the winter, with water filled pumps and an uninsulated door.
Just a thought,
Plumbing is not meant to be on an outside wall.
Better to keep all plumbing in an insulated cabinet
and have the heat in the cabinet radiate through the shell, and if the shell has no insulation on it, the shell
will transfer the heat into the tub and if the power goes out you have 4 - 5 hundred gallons of hot water which can radiate back into the cabinet.
hope this helps,
Don