As Martyn has said, use a good Polymeric or Cast and you will be fine mate. Cast always means that your giving as good as should be expected, but many fleet branding companies will use Polymeric and some even unlaminated monomeric.
We used to do milk tankers like this years ago and the big issue was “milk”. where the guys pulled the big milk hose onto the hole port to fill the take, it was spill milk around it and down the sides. for whatever reason, this would eat under the vinyl and it would start to peel back or pocket milk underneath and create a mess. always only happened around these ports for filling the tank. so content spills must be taken into consideration too.
make sure you trim at least 5mm away from the welds and fixings because the shape of the tank means all water and crap while driving is constantly pouring down the sides and catching in these areas. so dirt and grime catch and can make the vinyl come away over time.