I don’t really understand why you haven’t considered even discussing doing something less environmentally unsound.
You’ve taken the facts of the situation and decided to go ahead anyway.
There is an over riding factor in all this and that’s the fact that it’s a rubbish challenge and I know you will look back after doing it and agree that it wasn’t worth the cramped, sleepless car journey between each leg all for a couple 100 quid for a random charity that has nothing to do with the challenge itself.