Safety Petrol canisters

I come this summer, among other things, through the Karakum desert. Since there are not very many gas stations there I am dependent on having 20-40l petrol in canisters. Therefore my question: is it worrying (apart from the usual safety concerns to have petrol in a canister in a car) to carry petrol in a canister at 45-50°C air temperature? Are there differences between plastic and metal canisters?