Peter Fogwill has developed an "out of the box" alternative to the L5. It should be released in the next week or so, and apparently is fully CE marked, has a frost protection system (major advantage over the L5), doesn't require a modification to work at a low flow rate, and comes in a kit with all you need to vent it through the van roof.
I don't have personal experience of Peter's system,.. but I reckon its worth waiting a week before you choose!