If you want to use it then go ahead and use it. But it's going to add extra weight to your plane. Looking over your build you already have a lot of extra weight will all the extra epoxy and fillets your are using. While it may not seem like it all that weight adds up and adds up quick. Your result is going to be a heavy poorly flying plane. I'm not sure why you are adverse to the spackle. It's very cheap (around a buck or so if I remember correclty). </p>

Ken</p>

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