I marshal for Rat Race occasionally, and if the Crossing’s anything like Road Trip was last year, the catering van was open in the morning doing porridge pots as well as bacon butties. I don’t remember any charging points being available, but that may have changed.
All their bike events as far as I remember have had a secure storage area, but they tended to recommend having a cable lock with you anyway – people occasionally stopped at village shops, pubs etc for an extra top-up and it was worth having a ‘deterrent’ lock just in case. Same goes for overnight I guess, just a double protection.
You should get a better response by email though, hopefully!.