Good thoughts from Tim.
Also, have you tried what sales-people call the 'presumptive close'?
i.e. phone the venue where the course is, and tell them that you will be coming in your EV, and bringing an extension lead, and ask where you will need to put the EV in order to be able to charge up
I have found that working on the assumption that it WILL be possible often encourages training/hotel venues to make it possible.
With hotels, when I tell them I can't stay there unless they can let us charge up, they always find a way
Worth a try?
De Vere venues hotels have been most helpful in this regard.