pop rivets
On the forward most holes shown on your photograph (the ones with the #30 clecoes) I would use the rivets called out or screws. If you use pop rivets on the sides where you have the #40 clecos, to the rear of the #30 holes, you will have to enlarge the holes in order to be able to use cherrymax rivets. They don't come in 3/32, #40 size. And I don't think there are any 3/32 pop rivets that have the length, strength and intergrity that you need. (IMHO) I wouldn't use anything other than cherrymax or solid rivets. Many of us on these forums are first time builders and are giving our opinions where experts might be a better source. I would call Vans and ask them this question also. Jack