Garath, something worth considering is your towing limit on your 406 and whether its enough. The limit can be found in the user manual I think.
We towed our 200sx a couple of times to tracks and you have to be a bit careful of towing weights, if you want it all legal?
Your 335 touring probably weighs 1300kgs? and a suitable trailer to carry that would weigh about 4-500kgs(twin axle jobby) so that totals 17-1800kgs which is A LOT. We towed the sx with a mondeo TDCI estate and that has a very high limit for what is essentially a normal road car. Its limit is 1950kgs off the top of my head, i don't think your 405 will be that high though.
We used a local company, and got a deal for £25+ vat + straps for a days hire, which is pretty cheap to be fair. Normal price would have been about £40+ vat +straps. So there is a margin to be had. GO along the lines of, i'll probably be using your trailer service at least once every month to get my track car to events. Then you should be able to get a fairly good deal, even if you only intend to use it once
2cents
Jon