Water in a Wing

I bought a getaway with wings. When it arrived here one of the wings had (sea) water in it (about half a litre) which would not drain out.
I took one of the black aluminium ends off and took out the hard foam stopper to drain the water and flush the wing.

We put back the stopper with silicone and smeared some black "rubberized undercoating" asphalt based stuff on it for sealing.
(Hobie uses a similar stuff, it seems.)

Now, we only had aluminium pop rivets at hand and used these.
We assume the original ones (3/16") are SS, aren't they?
What grip length should I get (3/8"?) in case it is recommended to replace the ones we used?
Saludos

Stainless is for shear strength, so is recommended.

There are 1/4 and 3/8 rivets used in the seat assemblies. I'd guess the longer ones are used in the leg assemblies.

_________________
Matt Miller
Former - Director of Parts and Accessory Sales
Warranty and Technical Support
Hobie Cat USA
(Retired 11/7/2022)