I've got a 250L tank fitted and I can just about get 5 hours per day out of it, if I trad the downstairs on a few of the cleans.
I like tradding but it's so time consuming and I find it frustrating.
I would certainly get a 500L tank next, as I constantly worry about running out. You can carry a couple of 25ltr barrells and top up if you've got room in the cab of your van.
Unfortunately I've only got an Escort 55, so I can only carry 1 barrell on the floor by the passenger seat.
Experience tells me bigger van and bigger tank needed next time round.