We have had "issues" on this since we bought our 177 back in February 2011. First found out about this when we were camping in the U.P. in May of that year. Woke up with about a dozen mosquito bites and about 50 more inside!!! I thought I must of left the door open; quickly realized that the ONLY way for them to enter was through the breaches you mentioned. I have used both duct tape and an old t-shirt - both took care of the problem. I have used the t shirt option since the first year since it is reusable (the tape loses its stickiness after one or two uses). The only potential problem would be if you FORGET to remove it before closing the slide. Haven't tried that option yet and hopefully my memory will prevent me from trying it.
We have been camping with our 177 for 4 seasons now and the only times I use the t-shirt to close the breaches is if we are in snake country or in very buggy conditions, otherwise I leave it as is w/o any problems.
Edit: removed the ton of javascript and css that appeared below this text - any ideas where that came from? - techntrek