AW: Multiple RT3 Instances on 1 box?

we have different instances and even different versions of rt
running on one machine. 1.0.5, 2.0.11 and 3.0.4
So every rt has its one url like

One Apache is listening to port 80 and handling lots of
virtual hosts via mod_proxy and ReWriteRules to the other
instances running on ports like 13000, 13100, 13200, …

All of them work fine, the only problem are the PERL Modules.
When I installed rt 3.0.4 the CPAN module HTML:Mason was
updated to 1.20 so our rt 2.0.x were not running anymore
because they need HTML:Mason 1.05.
We had to downgrade the Parser Module to get everything back.

Ritschi =B-)