How much gas will I need?

Hi, we are new members and complete novices, hiring a motorhome for the first time this summer to spend approximately 18 days touring in Europe, staying at CC sites at each stop. The Autotrail Cheyenne 660 will be equipped with two full gas canisters by our very friendly hirer. Will that be ample/OK/not enough for two adults? We do a fair bit of cooking and both like a shower at least once a day, but will make use f the electric hook up at each CC site. If insufficent, whats's the best solution: are we better to take another canister, buy a conversion valve for European usage or any other solution we don't know about?! Thanks in advance for helping two eager novices! Andrew and Sarah