I am one of the VERY fortunate ones who was able to use ShipKiller's DIY to do mine and save a pant-load of cash (thnx again Ship!!!
) ..... I find it VERY hard to phathom that this can be done without removing the top as I had a heck of a time just dropping into the trunk to remove the hoop - not sure how they access & free the housing (unless doing it blind).
I was, however, able to do it without removing the whole top - I raised the driver's side up just enough to access the motor, probablly not recommended (as removing entirely is the safest bet) but I was a 1 man team at the time.
As for keeping the drains clean, I suggest a monthly visit in that department depending on your possible contaminants; I always seem to dig/push something out of the drains on a monthly basis.
I've learned that the trick to this is to wash the car, then come back to it about 20-30 minutes later and see if you still have a puddle developing fwd of the rear wheel wells .... if so, your drains aren't draining well enough.