The stiffeners would help.

For the coroplast hinging method normally done on SPADs (inserting the ailern stock between the upper and lower skins) I carry the upper wing skin back to cover 2/3 of the hinge flute. This reduces the flexible section from 4 mm to appx 1 mm. Then aftter the CA is cured, I crease the hinge line up and down to 90 deg deflection a few times, so the hinge line moves freely. The stiffer hinge line gives reduced flutter tendancies.

Unfortunately, I have not found a good method to stiffen the coro hinge line at the tailplanes when using a single thickness of 4 mm. I've been considerng putting up with the added weight of 2 layer 2 mm to do an airfoiled shape tailplane and get the stiffer hinges... There are some aerodynamic benefits. But my coroplast planes tend to come out tailheavy already and I hate adding ballast. I may try this when I make my replacement fuselage for my 4*60 though... it has fairly large surfaces and needs more stiffness than 1 layer of 4 mm