Mike,
A trailer sailer around 22 ft long should have a rig towing weight of less than 2 tonnes (2000 kilos or 4400lbs). One way to estimate your total towing weight is to get the displacement of your boat in pounds or kilos and add 50%
I recommend you watch the video here
http://www.sailingmates.com/salespublic.htm where I touch on trailer towing weights and some of the other things you need to think about.
You could always buy the boat buying manual at the link if you wished. At $17 it;s a steal

. There's a detailed video and pdf covering trailer sailers in general and in particular towing weights and hitches and the many other things you need to consider carefully when you set up your trailer and vehicle
peter