Spray foam won't help the climate control that much...you have 6" between the rafters and drywall...it's probably already insulated with fiberglass...have you confirmed?

I am currently replacing an older tile shower with a fiberglass enclosure. 

Are most pool cabins being built fiberglass, vinyl liner, or gunite pools? 

Are the fiberglass granules starting to delaminate?

Is a fiberglass epoxy liner worth having for our transition pipes?

Renter rents unit with Jet Tub, fails to clean it properly, (Believes) medical condition is caused by failure to clean tub properly, asks owner for standard tub in it's place due to not wanting to follow proper cleaning procedures.[1] In the future, the owner should add proper cleaning procedures to lease wording to give renters a heads up on this.[2] When showing the unit, disclose the proper cleaning procedures to potential renters (to give them a heads up).[3] Unless it is needed to compete for market rent in the area, consider the possibility of replacing it (HUD gives a service life for fiberglass tubs as 40 years, but that's just the tub and not the jet equipment or heaters--which may be less and require costly repairs/replacement).[4] There are homeowner hacks for covering up the jets on YouTube, but I'm not sure they would be high enough quality for a rental.

It has typical fiberglass insulation.  

It's fiberglass and is an original with the house (built in 1973).

Was told that it was a more effective/long lasting option for a crawl space where over time the fiberglass insulation would fall/still have space for air to travel through. 

Also build walls with 2x4 studs (and a door) around the furnace and insulate the walls with 3 1/2" fiberglass.