Buying/securing a tank

I'm switching some of my work over from traditional to wfp and so I will be hoping to be using it approx 15hrs a week (not all customers will have it). I also don't really want to fill up more than once per week as will be getting the water from someone I know. I have a Peugeot Bipper that will take up to a 350l tank, but I could get a 250l tank and save some van space (it will be pretty cramped in there). I was just wondering what peoples opinions were? Would I regret not going for the biggest tank I can fit?

As for securing it, I will probably use ratchet straps on the floor loops. Would these do the job?

Appreciate any advice. Regards, Lloyd.

Ratchet straps are fine, l use them for a 650l tank, but buy the heavy duty industrial ones. Wfp is addictive, in my opinion, you will regret a small tank