MAD Progressive Springs

Hi, 
I tow my caravan with a Passat estate and I have fitted MAD progressive spring helpers to the rear suspension. This has not altered the ride height or enhanced the appearance of the car, increased the load capacity or performance. It prevents the rear of the car from sagging when I tow making it safer and easier to drive. The 'van is nicely matched to the car in terms of weight but the rear overhang and soft suspension causes the back to go down and the nose to rise. I have not altered the original springs - the new ones simply fit inside them.

It has just occurred to me that I should probably speak to my insurer about my new spring helpers, probably should have done so before, but never gave it a thought.
Does anyone have any tips on declaring this 'mod' to someone in an insurance call centre without giving them the impression that you a reverse mounted baseball cap wearing boy racer modding up his or her car for burn outs in Asda car parks?

I am thinking of writing to my insurer and enclosing the brochure I have, which will hopefully help me to convince them that I am not trying to be the Stig in my diesel Passat and that I'm trying to stay safe. I'm not looking to pull the will over their eyes, but by the same token I don't wish to stitch myself up.

Any tips or experience appreciated.