One thing I try to do as Germany is to attack that trn off Canada, I leave sz 109 alone. (it can be covered by 4 scrambling aircraft)
This does two things, it prevents the canadian armor from coming to UK, if UK wants to counter these subs they have to go way out to canada and any aircraft will not be able to return in time. Also as Germany I would rather leave the trn alive off England than Canada. Best case scenario UK weakens their london defense by pulling 2 units off! I also hit the BB/DD so that UK is left with only 1 dd alive UK1.
I think the best way to counter sealion with UK is to purchase 2 CV’s UK2. 32 ipcs, which should be possible with UK’s income, combined with the Med fleet means that Germ cannot invade London, provided you can block off Scotland.