[ZeroID (Brent)]

2" Focusser and the secondary is a generous one. I only need about another 3-4 mm but that is already stacked up on the adjusters so I will pull some of the neoprene supports out and use the box section to get it into position.

I think the sealant is better because it is designed for some thickness and setting as a volume whereas the adhesive works better as a thin film. The thickness is part of the flexible no-stress support structure. You would lose that with a thin film I'd think.

I've seen no corrosion problems with Alum and Sealant but if you want to be sure of a hold drill a hole where the sealant will be and squeeze a 'button' through to lock it on the far side. I did this with my lateral side supports. In fact I drilled the hole and set the support about 2 mm from the side and then squeezed the sealant through the hole to the mirror edge tofill the gap, very tidy looking.