[The Jester of Wibbly]

https://amzn.eu/d/gJxptzC

And it's cheap too.  Silver/Black 260 GSM Tarpaulin Waterproof Heavy Duty Tarp Sheet Cover.  ( Needs to be the Silver/Black as that's the thicker one.   I bought the 3x4m one, folded in half for even better protection.  It covers my tank and real in full.   

It's not going to fully protect you, but mines kept everything toasty and protected in -3 night conditions without issue.