Horsefield tortoise bath time

Here's my tortoise Colin getting warmed up in a sink bath. I've had him 6 years now but he has never hibernated. When he first came to me he'd been fed on a high protein diet which lead to his shell 'pyramiding' and growing rapidly, disproportionately to his actual body mass.
This means I couldn't be sure of his weight and whether he'd survive hibernation... Not something I want to risk.