I kept my tubs closed with bungee cords, but I've seen racks built so that the tub takes up the whole slot so you cannot open the lid unless you slide the tub out. I'm on my phone right now so link searching would be difficult, but there are definitely threads for DIY tubs on here. Hopefully someone on a computer can link to some.

And yes, mikoh4752 is right. I was writing this at 2am last night, I guess my brain was already asleep lol. What I meant was that BCI=Boa constrictor imperiator, and that my recommendation was for the BCI Colombian RTB, since that's the subspecies I own and am familiar with.