I only ever remove my tank when it I want to use my van for a camping trip with the family. When I do it has to be totally empty which does not always fit in with the work I have bee doing, so I either end up wasting water or pumping it in to another van.
I think If you need to take you tank out on a regular basis it will be a right pain. Have you considered having a custom low profile tank made which can act as part of the van floor. I think you can get custom tanks through Gardiners.
All that said though I use my van for window cleaning, carpet cleaning, gutter cleaning and pressure washing. I think I could fit all the gear in the van at once, at a push, and I use a 500l tank in a Renault Traffic. So maybe you won't need to remove the tank after all.