Page Comparison

[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)

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 stress results are no where close to yield strength.

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