Hi ,yeah it's really worth it to do the two series in parallel .
In just series ...the time it takes for the suction to reach its max is quite slow , every time u lift the wand it has to build up again .
Where as if you add the port and put each series machine in parallel u increase the airflow ...the result is the suction max rises almost instantly ....it's a much nicer suction to use.
So why not just use parallel u might ask ... parallel will have a fast suction rise ...but it doesn't have the hard vacuum pull on the carpet u get with both series /parallel .
For the sake of drilling a hole it's really worth it ...the steambrite link above is really for a vertical mount through a lid... Not practical for the enforcer ....the best spot is at the side near the top ... But u could use it , no need for the cage ...but it's just a couple tank bulkhead fittings and z cap u can source for a few £ from plumbing stores.