[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.

[Simon Trapani]

That won’t do anything of note imo.

Can’t beat an oil filled rad with stat on low.

[windowswashed]

I bought some of that 10mm rubber insulation with a silver backed foil with the really sticky backing, that is very good for insulating the tank and the R/O out in the garage.

[Scottish Cleaning Service]

I have an 18Tog Duvet around my tank, for less than a score for the King size.

https://www.ebay.co.uk/itm/157017072825?var=458513889122&_ul=GB&mkevt=1&mkcid=1&mkrid=710-53481-19255-0&campid=5339069422&toolid=20006&customid=CjwKCAiAuIDJBhBoEiwAxhgyFu1Me2wLwP_JOmkFLPhGsnNy7wID19iJ2mz3IeAcM4xwE5EWLXjM-BoCDcIQAvD_BwE%7C0AAAAA9SEzLOQHCT4odmBAqziiy9rZu1n7%7Cnull&gclid=CjwKCAiAuIDJBhBoEiwAxhgyFu1Me2wLwP_JOmkFLPhGsnNy7wID19iJ2mz3IeAcM4xwE5EWLXjM-BoCDcIQAvD_BwE&gbraid=0AAAAA9SEzLOQHCT4odmBAqziiy9rZu1n7&loc_physical_ms=9046957&adtype=pla