A few years back I went over to a pick up thinking it would be better than a van. You can't carry as much imho and as others have said most leak or aren't water tight. If you have rear seats in it you can't claim 100% to tax as hmrc will argue you could use it for social use. Ultimately I crashed it and it rolled 4 times over. The rear canopy burst off and I lost most of my tools. Whilst it saved my life it was a good opportunity to go back to a van.
A word of warning for anyone looking at pickups direct or vanarama. We leased another pickup from this company. The Truckman back leaked like a sieve from day 1 and they did nothing about it. The whole compliant rumbled on for 4 years and ultimately they had to pay us huge amounts of compensation because the financial ombudsman forced them too.
Having tried both I feel a van works better for me for work, on a day to day basis.