I was into the same problem gluing plexi to fiberglas.
I do know that one of the "Sika" products can do the job, but PU body sealer single component can do the job too.
But make sure that the sealer has a little thicknes.. so it can take temperature moves from the diffent materials...
I think that in evry country there is an officiel inspection for construction at home of aircrafts, I know for sure there are here in Denmark. They will tell you what kind of inspection there is needed and what tests that have to be done during the construction.
Most homemade airplanes start out...
