Towbar load weight for the Rav4 is 60kg for the petrol versions and 80kg for the diesel. That's from 06 onwards models (they call it the 4.3 version) don't know what the earlier ones might be. No problems with mine (a 57 reg)lovely motor to drive solo and towing.
The earlier 4.2 version could have a problem with the dual mass flywheels fitted to them,the flywheel bolts started breaking up resulting in a very expensive repair bill, didn't affect all but a fair few. Toyota extended the warranty to 5 years to cover 00-02 models that were affected and changed the flywheel design in 03.
The 4.3 models don't have any issues I know of. Only thing that keeps coming up in the owners club is the high cost of spares and repair to tyres on models that aren't fitted with a spare wheel. Those without use either special run flat tyres or just have an aerosol for temporary repair. Made sure I got one with a spare on the back door, don't fancy towing without one and being stranded because not all Toyota dealers have the facilities to change the run flats, it's a unique machine they need so you can't get it down at normal tyre centres.