Richardson,
Nice looking van, but a bit of a dilemma for you, I believe they have done it before and they do protect their copyrighted logos quite vigorously.
If you do ignore them and they decide to proceed down the legal route and win their case, then you will probably be liable for their costs.
We bought a second hand Thermopure system in a liveried Renault Trafic, it originally had the full wrap photo's on along with the wfp man, took the wrap off but left the logos on as they do look very effective.
Before buying their van I had an artist make up a similar picture to the Ionics man to put on our original WFP van (non ionics), but was advised that their logo was copyrighted and I shouldn't use it.
What's the saying "Imitiation is the greatest form of flattery"!!