I would use Beer Line Cleaner for about £6/ 5 Litres - it works by soaking the racks in COLD water and leaving them for at least 24 hours or longer if you have the time to do this....
It is non-caustic, and non-toxic, don't let it splash onto your clothes as it will stain like bleach.
then afyer they have soaked for 24 hours or longer remove baked on protein and carbon from the racks in hot soapy water with steel wool. polish afterwards to a shine.
Easy.
you'll need to buy a soaking tray - Lakeland Ltd sell large blue trays for about £20 and they are deep, lightweight and will sit in the ack of your van holding everything in place till you need it..