They came in and used material that has fiberglass and left it all in the floor of the basement.

Looking at wood or fiberglass replacements.

I found using a dremel worked well to grind out a recessed area to place fiberglass tape at cracks. 

@Drew Dowdell so there are some fiberglass products that are carried by the Home Depot that are similar. 

Took out about 5 inches of drywall across three feet and the wall feels solid everywhere else except where the drywall meets the fiberglass tub/shower combo.

Just spoke to my handyman & he said that (as Greg B. stated) mobile home doors are odd sized & a combination Aluminum & Fiberglass in many cases. $400 is about right according to him.mobilehomeparts.com is a website that my handyman uses to fix his mobile home client's units.

Then install "Vinyl" railings and Balusters (low upkeep).Have the front steps built like this (so they don't look like your looking through a skeleton).Put in a Fiberglass (low maintenance) Large Oval Glass front door with a good looking lock handle.Then I'd get rid of the vertical slider windows upstairs and replace them with ones that match the downstairs windows.

Open cell foam will work but only marginally (just a bit) worse than rock wool or fiberglass.

Tiled over old tile in pan (had existing fiberglass pan liner) after mechanical abrasion of tile...used a diamond tile bit and scored the tile.

Assuming it's not an A+ luxury unit in the most desirable part of town, then I'd usually recommend a plastic shower curtain instead of a glass door, because it costs much less and can be changed easily between tenants (whereas a glass door often accumulates water spots that can be difficult to fully clean after a few tenants...and, as you mentioned, if a tenant breaks a glass door, that could be a costly headache).Also, assuming it's not an A+ luxury unit, I'd usually recommend going with a fiberglass unit (either tub or shower) instead of tile, because tile is usually more expensive, and it can be more likely to begin leaking, and it requires more upkeep.