Tub Gap Sizes and Sagging Concerns

[pet_snake_78]

I've built my first rack out of 1/2" redwood plywood, treated with two coats procrylic. I used a dremel to make a place for the probes at the back. I used framing studs for the side supports and 1x3's for the interior wooden pieces since they were some of the straightest boards in the store. Everything went together easy enough, although a 4' tall wooden rack is pretty hard to flip over by yourself!

I have two concerns, some people say plywood sags but others seem to indicate it only sags if you don't have all the slots filled with tubs. Anyone have first hand experience over time? My second concern is that my gaps are way too large, I can almost fit my pinkie between the gap and the top in a couple of places. I want to put caulkers cays in them but they are only around 3' and not very thick. It seems like only a huge snake couldn't escape? My biggest fear about switching over to racks has been escapees.