Okay Lars. I was a bit worried because about 25 years ago I've worked with the (old) Nacra tubes when restoring a Patin a Vela cat.
Replacing its fixed wooden bridge by mountable aluminium beams, which were by the way half of your length!
I was given for free a bunch of damaged Nacra beams by Jan de Boer, the dutch Nacra importer.
He had a lot of those beams standing in a corner, all damaged or broken off just where the dolphinstriker is attached next to the hull.

In order to correct that failure Nacra has later on started to use more inside enforcement, especially in that place. So, it is stricly speeking not an overkill to use sleeves inside.
Galvanic corrosion stays a problem however at that particular place.

In the modern F-cats from Nacra there is a considerable enforcement inside the beams but I don't know if that goes all the length or just by short sleeves.

Bon courage with the restoration.