CC Materials/Manufacturing/Assembly Detailed Design

[1] Acrylic
Yield Strength: 64.8 - 83.4 MPa (Average value: 75.4 MPa)
Young’s Modulus: 2.76 - 3.30 GPa

Flexural Modulus: 2.96 - 3.30 GPa
Flexural Yield Strength: 98.0 - 125 MPa (Average value: 109 MPa)

[2] PETG
Yield Strength: 28.3 - 58.6 MPa
Young’s Modulus: 1.10 - 20.3 GPa (Average value of 2.65 GPa)

Flexural Modulus: 1.17 - 2.76 GPa
Flexural Yield Strength: 39.2 - 88.9 MPa (Average value of 69.5 MPa)

In short, Plexiglas is a strong enough viable alternative for the side walls of the cover.

Gel-coat
Protective finishing layer for composite surfaces.
Leaves a hard smooth surface good for sticking on adhesive.
Requires sanding and buffing for a smooth surface.
If painting the cover, apply gel-coat first then paint over it.

Source:
[1] http://www.matweb.com/search/datasheet.aspx?bassnum=O1303
[2] http://www.matweb.com/search/datasheet.aspx?matguid=4de1c85bb946406a86c52b688e3810d0

Assuming quarter inch thickness of all fiberglass (no foam core).
This is to make calculations easier, results might be the same with a foam core or even better.

Fiberglass composite flexural strength- 350Mpa.
Fiberglass board of dimensions 0.7m x 0.5m x 0.00635m.
2 x 70kg humans acting as force.
3 point bend test.

Result stress is 72MPa using formula below.
Stress is less than yield strength.

Which means a quarter inch thickness is more than enough and could be thinner.
Note that results are theoretical, but results are no where close to yield strength.

Deflection at load point (more math):

Standard epoxy resin is a good choice for fiberglass.
Has heat resistance of up to 150C. Enough time for occupants to escape vehicle in a thermal runoff situation.

Resins in general melt polystyrene and styrofoam foams so they cannot be used.
Polyurethane foams are a good alternative.

Foam are bought in large thick sheets, they can be cut down into size using hot wire foam cutter.
Composites Canada carries urethane foam which is a good place to buy from.