Well, I have scrapped the runners on the bottom of the trays. It just didn't work out for me and the cheap epoxy that I used. Maybe some better glue would've worked...? What I've done is add a strip of wood on top of the shims so that the lip of the oil tray rides on it close to the bottom of the bottom board. There's no way that a bee can get through the gap between the tray and bottom board. I like this setup better.
I actually added some thin shims to this but I think it was good enough like this.
Something else I did was address the "ledge" along the sides of the bottom board that the screen is stapled to. My concern was that a beetle or mite could land on that flat ledge and climb back up. I added the triangular pieces of wood figuring they might help to direct the "bounce" of the pest out onto the screen over the oil tray. The back ledge is much smaller so I added nothing to it. Here's a couple of shots of ISOT with some "bling" added to it.
Hopefully I can slip this board under one of my hives this weekend and start testing it out. Oh, I almost forgot...the issue of water entering the oil tray. I've was going to order a Sunsetter retractable awning :-D but decided instead to put a metal awning up. I don't have a picture of it, but it's simply a sheet of flashing several inches wider than the hives are wide and only about 6" long. It is bent at a 90-degree angle the length of it so that one leg of the bend is long enough to extend over the edge of the porch. Three frame nails or staples and it's attached to the front of the hive. I crimped the long edges and folded and crimped the corners...it is rigid enough to handle a heavy rain. We'll see how it works...
The next ISOT will hopefully be much cleaner than this one as this was the trial-and-error one. All of this is probably overkill, but with only a few hives I can afford the luxury of tinkering. Hopefully, by the time I build up my hive count I will have streamlined these mods....if they work.
cerezha, thanks for the doublesided tape and political sign suggestion. I'll keep that in mind...it may even work as the added shims.
F.W., the awning may do just what you were talking about in directing the beetles down to the "first level" where the screen and slits are.