You can have cellulose/fiberglass blown into the joists.

Then wood deck over the top.The master tub is fiberglass.

I toyed with the idea of pulling the toilet and cutting a hole in the front apron of that fiberglass tub, but really didn't want to do that.

Old toilets and fiberglass tub/showers?

The original fiberglass were not doing its job.

Fiberglass  can hairline crack and reglazing can address this.  

(For this same reason I rarely use a fiberglass surround).

I can repair almost and damage, weld tub holes and fill them, repair the WORST fiberglass cracks, broken tiles, Its not an ad here and I am not trying to push my company, but I literally have 2.33 in my checking with a $3000 mortgage payment coming up, and I am getting desperate.

I noticed that my fiberglass batt insulation up in my floor joists isn't looking that effective (it's from 1993 and needs some work to get back to adequate).

Houses had no fireplace, vinyl and carpet, no microwave, white appliances, 7-8 windows, flat doors, 3 sides brick, 30" upper cabinets, wilsonart counter tops and fiberglass tub/shower enclosures.